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  • 1.
    Akanda, Nesar
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Biophysical properties of the apoptosis-inducing plasma membrane voltage-dependent anion channel2006Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 90, nr 12, s. 4405-4417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion channels in the plasma membrane play critical roles in apoptosis. In a recent study we found that a voltage-dependent anion channel in the plasma membrane (VDACpl) of neuronal hippocampal cell line (HT22) cells was activated during apoptosis and that channel block prevented apoptosis. Whether or not VDACpl is identical to the mitochondrial VDACmt has been debated. Here, we biophysically characterize the apoptosis-inducing VDACpl and compare it with other reports of VDACpls and VDACmt. Excised membrane patches of apoptotic HT22 cells were studied with the patch-clamp technique. VDACpl has a large main-conductance state (400 pS) and occasionally subconductance states of µ28 pS and 220 pS. The small subconductance state is associated with long-lived inactivated states, and the large subconductance state is associated with excision of the membrane patch and subsequent activation of the channel. The open-probability curve is bell shaped with its peak around 0mV and is blocked by 30µM Gd3+. The gating can be described by a symmetrical seven-state model with one open state and six closed or inactivated states. These channel properties are similar to those of VDACmt and other VDACpls and are discussed in relation to apoptosis.

  • 2.
    Akanda, Nesar
    et al.
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi.
    Tofighi, Roshan
    Karolinska Inst, Dept Neurosci, SE-17177 Stockholm, Sweden .
    Brask, Johan
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi.
    Tamm, Christoffer
    Karolinska Inst, Dept Neurosci, SE-17177 Stockholm, Sweden .
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Ceccatelli, Sandra
    Karolinska Inst, Dept Neurosci, SE-17177 Stockholm, Sweden .
    Voltage-dependent anion channels (VDAC) in the plasma membrane play a critical role in apoptosis in differentiated hippocampal neurons but not in neural stem cells2008Inngår i: Cell Cycle, ISSN 1538-4101, E-ISSN 1551-4005, Vol. 7, nr 20, s. 3225-3234Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    microRNAs (miRNAs) are small non-coding RNAs that regulate a large variety of cellular processes including differentiation, apoptosis and proliferation. Several miRNAs display defective expression patterns in human tumors with the consequent alteration of target oncogene or tumor suppressor genes. Many of these miRNAs modulate the major proliferation pathways through direct interaction with critical regulators such as RAS, PI3K/PTEN or ABL, as well as members of the retinoblastoma pathway, Cyclin-CDK complexes or cell cycle inhibitors of the INK4 or Cip/Kip families. A complex interplay between miRNAs and MYC or E2F family members also exists to modulate cell cycle-dependent transcription during normal or tumoral proliferation. The ability of miRNAs to modulate these proliferation pathways may have relevant implications not only in physiological or developmental processes but also in tumor progression or cancer therapy.

  • 3.
    Asif, Muhammad
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan. COMSATS institute of Information Technology, Lahore, Pakistan.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Electrochemical Biosensors Based on ZnO Nanostructures to Measure Intracellular Metal Ions and Glucose2011Inngår i: Journal of Analytical & Bioanalytical Techniques, ISSN 2155-9872, Vol. S7, nr 003, s. 1-9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zinc oxide (ZnO) nanostructures have attracted much interest for intracellular electrochemical measurements because of its large surface area, and its biocompatible properties. To design intracellular biosensors for metal ions and glucose, we grew ZnO nanorods on the tip of borosilicate glass capillaries (0.7μm in diameter) and characterized the nano-scale structure with field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The ZnO nanorods were functionalized accordingly for intracellular free metal ions or glucose measurements. Selectivity was achieved by using a metal-ion selective plastic membrane or glucose oxidase enzyme for glucose measurements. These functionalized ZnO nanorods showed high sensitivity and good biocompatibility for intracellular environments. Human adipocytes and frog oocytes were used for determinations of intracellular free metal ions and glucose concentrations. In this review, we discuss the simple and direct approach for intracellular measurements using ZnO nanostructure-based potentiometric biosensors for clinical and non-clinical applications. The performance of ZnO nanostructure-based intracellular sensor can be improved through engineering of morphology, effective surface area, functionality, and adsorption/desorption capability. This study paves the way to find applications in biomedicine by using this simple and miniaturized biosensing device

  • 4.
    Asif, Muhammad H
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Fulati, Alimujiang
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nor, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Johansson, Cecilia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Strålfors, Peter
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Börjesson, Sara I.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Functionalized zinc oxide nanorod with ionophore-membrane coatingas an intracellular Ca2+ selective sensor2009Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, nr 2, s. 23703-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The tip of a borosilicate glass capillary with functionalized hexagonal ZnO nanorods was used to make a sensitive electrochemical intracellular Ca2+ sensor. To adjust the sensor for Ca2+ measurements with sufficient selectivity and stability, polyvinyl chloride (PVC) membrane containing Ca2+ ionophores were coated on the surface. The membrane covered ZnO nanorods exhibited a Ca2+-dependent electrochemical potential difference versus an Ag/AgCl reference electrode. The potential difference was linear over a large concentration range (100 nM to 10 mM). The measurements of Ca2+ concentrations using our ZnO nanorods sensor in human fat cells or in frog egg cells were consistent with values of Ca2+ concentrations reported in the literature. This nanoelectrode device paves the way to measurements of intracellular biochemical species in specific locations within single living cells.

  • 5.
    Asif, Muhammad H.
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Strålfors, Peter
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Brännmark, Cecilia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Englund, Ulrika H
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Growth and Structure of ZnO Nanorods on a Sub-Micrometer Glass Pipette and Their Application as Intracellular Potentiometric Selective Ion Sensors2010Inngår i: Materials, ISSN 1996-1944, Vol. 3, s. 4657-4667Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the growth and structure of ZnO nanorods on a sub-micrometer glass pipette and their application as an intracellular selective ion sensor. Highly oriented, vertical and aligned ZnO nanorods were grown on the tip of a borosilicate glass capillary (0.7 μm in diameter) by the low temperature aqueous chemical growth (ACG) technique. The relatively large surface-to-volume ratio of ZnO nanorods makes them attractive for electrochemical sensing. Transmission electron microscopy studies show that ZnO nanorods are single crystals and grow along the crystal’s c-axis. The ZnO nanorods were functionalized with a polymeric membrane for selective intracellular measurements of Na

     

    +. The membrane-coated ZnO nanorods exhibited a Na+-dependent electrochemical potential difference versus

    an Ag/AgCl reference micro-electrode within a wide concentration range from 0.5 mM to 100 mM. The fabrication of functionalized ZnO nanorods paves the way to sense a wide range of biochemical species at the intracellular level.

  • 6.
    Asif, Muhammad H
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Usman Ali, Syed M
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nur, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Brännmark, Cecilia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Strålfors, Peter
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Englund H, Ulrika
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Danielsson, Bengt
    Pure and Applied Biochemistry, Lund University, Box 124, SE-221 00 Lund, Sweden.
    Functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose2010Inngår i: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 25, nr 10, s. 2205-2211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose. To adjust the sensor for intracellular glucose measurements, we grew hexagonal ZnO nanorods on the tip of a silver-covered borosilicate glass capillary (0.7 mu m diameter) and coated them with the enzyme glucose oxidase. The enzyme-coated ZnO nanorods exhibited a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference was linear over the concentration range of interest (0.5-1000 mu M). The measured glucose concentration in human adipocytes or frog oocytes using our ZnO-nanorod sensor was consistent with values of glucose concentration reported in the literature; furthermore, the sensor was able to show that insulin increased the intracellular glucose concentration. This nanoelectrode device demonstrates a simple technique to measure intracellular glucose concentration.

  • 7.
    Asif, Muhammad
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Usman Ali, Syed
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Nour, Omer
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Englund, Ulrika
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Functionalized ZnO nanorod-based selective magnesium ion sensor for intracellular measurements2010Inngår i: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 26, nr 3, s. 1118-1123Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ZnO nanorods were grown on a silver-coated tip of a borosilicate glass capillary (0.7 mu m in tip diameter) and used as selective potentiometric sensor of intracellular free Mg2+. To functionalize the ZnO nanorods for selectivity of Mg2+, a polymeric membrane with Mg2+-selective ionophores were coated on the surface of the ZnO nanorods. These functionalized ZnO nanorods exhibited a Mg2+-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode within the concentration range from 500 nM to 100 mM. Two types of cells, human adipocytes and frog oocytes, were used for the intracellular Mg2+ measurements. The intracellular concentration of free Mg2+ in human adipocytes and frog oocytes were 0.4-0.5 and 0.8-0.9 mM, respectively. Such type of nanoelectrode device paves the way to enable analytical measurements in single living cells and to sense other bio-chemical species at the intracellular level.

  • 8.
    Broomand, Amir
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Disintegration of the voltage-sensor paddle during potassium-channel gatingManuskript (Annet vitenskapelig)
  • 9.
    Broomand, Amir
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Large-Scale Movement within the Voltage-Sensor Paddle of a Potassium Channel-Support for a Helical-Screw Motion2008Inngår i: Neuron, ISSN 0896-6273, E-ISSN 1097-4199, Vol. 59, nr 5, s. 770-777Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The size of the movement and the molecular identity of the moving parts of the voltage sensor of a voltage-gated ion channel are debated. In the helical-screw model, the positively charged fourth transmembrane segment S4 slides and rotates along negative counter charges in S2 and S3, while in the paddle model, S4 carries the extracellular part of S3 (S3b) as a cargo. Here, we show that S4 slides 16-26 Å along S3b. We introduced pairs of cysteines in S4 and S3b of the Shaker K channel to make disulfide bonds. Residue 325 in S3b makes close and state-dependent contacts with a long stretch of residues in S4. A disulfide bond between 325 and 360 was formed in the closed state, while a bond between 325 and 366 was formed in the open state. These data are not compatible with the voltage-sensor paddle model, but support the helical-screw model. © 2008 Elsevier Inc. All rights reserved.

  • 10.
    Broomand, Amir
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Jerremalm, E.
    Karolinska Institutet.
    Yachnin, J.
    University Hospital Uppsala.
    Ehrsson, H.
    Karolinska Institutet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Oxaliplatin neurotoxicity - No general ion channel surface-charge effect2009Inngår i: Journal of Negative Results in BioMedicine, ISSN 1477-5751, Vol. 8, nr 1, s. 2-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background. Oxaliplatin is a platinum-based chemotherapeutic drug. Neurotoxicity is the dose-limiting side effect. Previous investigations have reported that acute neurotoxicity could be mediated via voltage-gated ion channels. A possible mechanism for some of the effects is a modification of surface charges around the ion channel, either because of chelation of extracellular Ca2+, or because of binding of a charged biotransformation product of oxaliplatin to the channel. To elucidate the molecular mechanism, we investigated the effects of oxaliplatin and its chloride complex [Pt(dach)oxCl]- on the voltage-gated Shaker K channel expressed in Xenopus oocytes. The recordings were made with the two-electrode and the cut-open oocyte voltage clamp techniques. Conclusion. To our surprise, we did not see any effects on the current amplitudes, on the current time courses, or on the voltage dependence of the Shaker wild-type channel. Oxaliplatin is expected to bind to cysteines. Therefore, we explored if there could be a specific effect on single (E418C) and double-cysteine (R362C/F416C) mutated Shaker channels previously shown to be sensitive to cysteine-specific reagents. Neither of these channels were affected by oxaliplatin. The clear lack of effect on the Shaker K channel suggests that oxaliplatin or its monochloro complex has no general surface-charge effect on the channels, as has been suggested before, but rather a specific effect to the channels previously shown to be affected.

  • 11.
    Broomand, Amir
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Österberg, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Wardi, Tara
    Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Electrostatic domino effect in the Shaker K channel turret2007Inngår i: Biophysical Journal, ISSN 0006-3495, Vol. 93, nr 7, s. 2307-2314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated K channels are regulated by extracellular divalent cations such as Mg2+ and Sr2+, either by screening of fixed negative surface charges, by binding directly or close to the voltage sensor, or by binding to the pore. Different K channels display different sensitivity to divalent cations. For instance, 20 mM MgCl2 shifts the conductance versus voltage curve, G(V), of the Kv1-type Shaker channel with 14 mV, while the G(V) of Kv2.1 is shifted only with 7 mV. This shift difference is paralleled with different working ranges. Kv1-type channels open at −20 mV and Kv2.1 channel open at +5 mV. The aim of this study was to identify critical residues for this Mg2+-induced G(V) shift by introducing Kv2.1 channel residues in the Shaker K channel. The K channels were expressed in Xenopus laevis oocytes and studied with the two-electrode voltage-clamp technique. We found that three neutral-to-positive amino-acid residue exchanges in the extracellular loops connecting transmembrane segments S5 and S6 transferred the Mg2+-shifting properties. The contributions of the three residues were additive, and thus independent of each other, with the contributions in the order 425 > 419 > 451. Charging 425 and 419 not only affect the Mg2+-induced G(V) shift with 5–6 mV, but also shifts the G(V) with 17 mV. Thus, a few strategically placed surface charges clearly modulate the channel’s working range. Residue 425, located at some distance away from the voltage sensor, was shown to electrostatically affect residue K427, which in turn affects the voltage sensor S4—thus, an electrostatic domino effect.

  • 12. Bruening-Wright, Andrew
    et al.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för biomedicin och kirurgi, Avdelningen för medicinsk cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Larsson, H Peter
    Kinetic relationship between the voltage sensor and the activation gate in spHCN channels2007Inngår i: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 130, nr 1, s. 71-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are activated by membrane hyperpolarizations that cause an inward movement of the positive charges in the fourth transmembrane domain (S4), which triggers channel opening. The mechanism of how the motion of S4 charges triggers channel opening is unknown. Here, we used voltage clamp fluorometry (VCF) to detect S4 conformational changes and to correlate these to the different activation steps in spHCN channels. We show that S4 undergoes two distinct conformational changes during voltage activation. Analysis of the fluorescence signals suggests that the N-terminal region of S4 undergoes conformational changes during a previously characterized mode shift in HCN channel voltage dependence, while a more C-terminal region undergoes an additional conformational change during gating charge movements. We fit our fluorescence and ionic current data to a previously proposed 10-state allosteric model for HCN channels. Our results are not compatible with a fast S4 motion and rate-limiting channel opening. Instead, our data and modeling suggest that spHCN channels open after only two S4s have moved and that S4 motion is rate limiting during voltage activation of spHCN channels. © The Rockefeller University Press.

  • 13.
    Börjesson, Sara
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Hammarström, Sven
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Lipoelectric modification of ion channel voltage gating by polyunsaturated fatty acids2008Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 95, nr 5, s. 2242-2253Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyunsaturated fatty acids (PUFAs) have beneficial effects on epileptic seizures and cardiac arrhythmia. We report that ω-3 and ω-6 all-cis-PUFAs affected the voltage dependence of the Shaker K channel by shifting the conductance versus voltage and the gating charge versus voltage curves in negative direction along the voltage axis. Uncharged methyl esters of the PUFAs did not affect the voltage dependence, whereas changes of pH and charge mutations on the channel surface affected the size of the shifts. This suggests an electrostatic effect on the channel's voltage sensors. Monounsaturated and saturated fatty acids, as well as trans-PUFAs did not affect the voltage dependence. This suggests that fatty acid tails with two or more cis double bonds are required to place the negative carboxylate charge of the PUFA in a position to affect the channel's voltage dependence. We propose that charged lipophilic compounds could play a role in regulating neuronal excitability by electrostatically affecting the channel's voltage sensor. We believe this provides a new approach for pharmacological treatment that is voltage sensor pharmacology. © 2008 by the Biophysical Society.

  • 14.
    Börjesson, Sara I
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    An electrostatic potassium channel opener targeting the final voltage-sensor transition2011Inngår i: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 137, nr 6, s. 563-577Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study we have localized the site of action for PUFAs on the voltage-gated Shaker K channel, by introducing positive charges on the channel surface which potentiated the PUFA effect. We furthermore found that PUFA mainly affects the final voltage-sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

  • 15.
    Börjesson, Sara I.
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Structure, function, and modification of the voltage sensor in voltage-gated ion channels2008Inngår i: Cell Biochemistry and Biophysics, ISSN 1085-9195, E-ISSN 1559-0283, Vol. 52, nr 3, s. 149-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels are crucial for both neuronal and cardiac excitability. Decades of research have begun to unravel the intriguing machinery behind voltage sensitivity. Although the details regarding the arrangement and movement in the voltage-sensing domain are still debated, consensus is slowly emerging. There are three competing conceptual models: the helical-screw, the transporter, and the paddle model. In this review we explore the structure of the activated voltage-sensing domain based on the recent X-ray structure of a chimera between Kv1.2 and Kv2.1. We also present a model for the closed state. From this we conclude that upon depolarization the voltage sensor S4 moves ~13 Å outwards and rotates ~180º, thus consistent with the helical-screw model. S4 also moves relative to S3b which is not consistent with the paddle model. One interesting feature of the voltage sensor is that it partially faces the lipid bilayer and therefore can interact both with the membrane itself and with physiological and pharmacological molecules reaching the channel from the membrane. This type of channel modulation is discussed together with other mechanisms for how voltage-sensitivity is modified. Small effects on voltage-sensitivity can have profound effects on excitability. Therefore, medical drugs designed to alter the voltage dependence offer an interesting way to regulate excitability.

  • 16.
    Börjesson, Sara I.
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Englund, Ulrika H.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Asif, Muhammad H.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Intracellular potassium (K+) concentration decrease is not obligatory for apoptosis2011Inngår i: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, nr 46, s. 39823-39828Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    K+ efflux is observed as an early event in the apoptotic process in various cell types. Loss of intracellular K+ and subsequent reduction in ionic strength is suggested to release the inhibition of proapoptotic caspases. In this work, a new K+-specific microelectrode was used to study possible alterations in intracellular K+ in Xenopus laevis oocytes during chemically induced apoptosis. The accuracy of the microelectrode to detect changes in intracellular K+ was verified with parallel electrophysiological measurements within the same cells. In concordance with previous studies on other cell types, apoptotic stimuli reduced the intracellular K+ concentration in Xenopus oocytes and increased caspase-3 activity. The reduction in intracellular K+ was prevented by dense expression of voltage-gated K (Kv) channels. Despite this, the caspase-3 activity was increased similarly in Kv channel expressing oocytes as in oocytes not expressing Kv channels. Thus, in Xenopus oocytes caspase-3 activity is not dependent on the intracellular concentration of K+.

  • 17.
    Börjesson, Sara
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Parkkari, Teija
    University of Kuopio, Finland.
    Hammarström, Sven
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Electrostatic Tuning of Cellular Excitability2010Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 98, nr 3, s. 396-403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels regulate the electric activity of excitable tissues, such as the heart and brain. Therefore, treatment for conditions of disturbed excitability is often based on drugs that target ion channels. In this study of a voltage-gated K channel, we propose what we believe to be a novel pharmacological mechanism for how to regulate channel activity. Charged lipophilic substances can tune channel opening, and consequently excitability, by an electrostatic interaction with the channels voltage sensors. The direction of the effect depends on the charge of the substance. This was shown by three compounds sharing an arachiclonyl backbone but bearing different charge: arachidonic acid, methyl arachidonate, and arachidonyl amine. Computer simulations of membrane excitability showed that small changes in the voltage dependence of Na and K channels have prominent impact on excitability and the tendency for repetitive firing. For instance, a shift in the voltage dependence of a K channel with -5 or +5 mV corresponds to a threefold increase or decrease in K channel density, respectively. We suggest that electrostatic tuning of ion channel activity constitutes a novel and powerful pharmacological approach with which to affect cellular excitability.

  • 18.
    Conti, Luca
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Renhorn, Jakob
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Gabrielsson, Anders
    KTH Royal Institute Technology, Sweden.
    Turesson, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin. Linköpings universitet, Medicinska fakulteten.
    Liin, Sara
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Lindahl, Erik
    KTH Royal Institute Technology, Sweden; Stockholm University, Sweden.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation2016Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikkel-id 27562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated potassium channels open at depolarized membrane voltages. A prolonged depolarization causes a rearrangement of the selectivity filter which terminates the conduction of ions - a process called slow or C-type inactivation. How structural rearrangements in the voltage-sensor domain (VSD) cause alteration in the selectivity filter, and vice versa, are not fully understood. We show that pulling the pore domain of the Shaker potassium channel towards the VSD by a Cd2+ bridge accelerates C-type inactivation. Molecular dynamics simulations show that such pulling widens the selectivity filter and disrupts the K+ coordination, a hallmark for C-type inactivation. An engineered Cd2+ bridge within the VSD also affect C-type inactivation. Conversely, a pore domain mutation affects VSD gating-charge movement. Finally, C-type inactivation is caused by the concerted action of distant amino acid residues in the pore domain. All together, these data suggest a reciprocal communication between the pore domain and the VSD in the extracellular portion of the channel.

  • 19.
    Danielsson, Bengt
    et al.
    Pharmaneti3, Sweden Uppsala University, Sweden .
    Danielsson, Christian
    Karolinska Institute, Sweden .
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Skold, Anna-Carin
    AstraZeneca RandD, Sweden .
    Pehrson, Richard
    AstraZeneca RandD, Sweden .
    Stockling, Kenneth
    AstraZeneca RandD, Sweden .
    Hellmold, Heike
    AstraZeneca RandD, Sweden .
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Sylven, Christer
    Karolinska Institute, Sweden .
    Drug induced embryonic cardiac arrhythmia: A teratogenic mechanism of human relevance in TOXICOLOGY LETTERS, vol 211, issue , pp S186-S1862012Inngår i: TOXICOLOGY LETTERS, Elsevier , 2012, Vol. 211, s. S186-S186Konferansepaper (Fagfellevurdert)
    Abstract [en]

    n/a

  • 20.
    Danielsson, C
    et al.
    Karolinska Institutet, Stoclholm.
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Sköld, A-C
    AstraZeneca R&D, Södertälje.
    Andersson, A
    Karolinska Institutet, Stockholm.
    Pehrson, R
    AstraZeneca R&D, Södertälje.
    Stockling, K
    AstraZeneca R&D, Södertälje.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Hellmold, H
    AstraZeneca R&D, Södertälje.
    Sylven, C
    Karolinska Institutet, Stockholm.
    Danielsson, B. R.
    Pharmanet Development, Stockholm.
    Is Cardiac Arrhythmia in the Human Embryo a Possible Mechanism for Cardiovascular Defects by I-Kr Blocking Antidepressants? in BIRTH DEFECTS RESEARCH PART A-CLINICAL AND MOLECULAR TERATOLOGY, vol 91, issue 5, pp 345-3452011Inngår i: BIRTH DEFECTS RESEARCH PART A-CLINICAL AND MOLECULAR TERATOLOGY, WILEY-BLACKWELL, COMMERCE PLACE, 350 MAIN ST, MALDEN 02148, MA USA , 2011, Vol. 91, nr 5, s. 345-345Konferansepaper (Fagfellevurdert)
    Abstract [en]

    n/a

  • 21.
    Danielsson, Christian
    et al.
    Karolinska University Hospital, Sweden .
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Skold, Anna-Carin
    AstraZeneca RandD Sodertalje, Sweden .
    Genead, Rami
    Karolinska University Hospital, Sweden .
    Andersson, Agneta
    Karolinska University Hospital, Sweden .
    Andersson, Ulf
    AstraZeneca RandD Sodertalje, Sweden .
    Stockling, Kenneth
    AstraZeneca RandD Sodertalje, Sweden .
    Pehrson, Rickard
    AstraZeneca RandD Sodertalje, Sweden .
    Grinnemo, Karl-Henrik
    Karolinska University Hospital, Sweden .
    Salari, Sajjad
    Linköpings universitet, Institutionen för klinisk och experimentell medicin. Linköpings universitet, Hälsouniversitetet.
    Hellmold, Heike
    AstraZeneca RandD Sodertalje, Sweden .
    Danielsson, Bengt
    Pharmanet Dev Grp, Sweden Uppsala University, Sweden .
    Sylven, Christer
    Karolinska University Hospital, Sweden .
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Exploration of human, rat, and rabbit embryonic cardiomyocytes suggests K-channel block as a common teratogenic mechanism2013Inngår i: Cardiovascular Research, ISSN 0008-6363, E-ISSN 1755-3245, Vol. 97, nr 1, s. 23-32Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several drugs blocking the rapidly activating potassium (K-r) channel cause malformations (including cardiac defects) and embryonic death in animal teratology studies. In humans, these drugs have an established risk for acquired long-QT syndrome and arrhythmia. Recently, associations between cardiac defects and spontaneous abortions have been reported for drugs widely used in pregnancy (e.g. antidepressants), with long-QT syndrome risk. To investigate whether a common embryonic adverse-effect mechanism exists in the human, rat, and rabbit embryos, we made a comparative study of embryonic cardiomyocytes from all three species. less thanbrgreater than less thanbrgreater thanPatch-clamp and quantitative-mRNA measurements of K-r and slowly activating K (K-s) channels were performed on human, rat, and rabbit primary cardiomyocytes and cardiac samples from different embryo-foetal stages. The K-r channel was present when the heart started to beat in all species, but was, in contrast to human and rabbit, lost in rats in late organogenesis. The specific K-r-channel blocker E-4031 prolonged the action potential in a species- and development-dependent fashion, consistent with the observed K-r-channel expression pattern and reported sensitive periods of developmental toxicity. E-4031 also increased the QT interval and induced 2:1 atrio-ventricular block in multi-electrode array electrographic recordings of rat embryos. The K-s channel was expressed in human and rat throughout the embryo-foetal period but not in rabbit. less thanbrgreater than less thanbrgreater thanThis first comparison of mRNA expression, potassium currents, and action-potential characteristics, with and without a specific K-r-channel blocker in human, rat, and rabbit embryos provides evidence of K-r-channel inhibition as a common mechanism for embryonic malformations and death.

  • 22.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Alpha and omega in potassium-channel opening2019Inngår i: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 225, nr 2, artikkel-id e13240Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    n/a

    Fulltekst tilgjengelig fra 2020-12-16 15:11
  • 23.
    Elinder, Fredrik
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Akanda, Nesar
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Tofighi, R.
    Institute of Environmental Medicine, Division of Toxicology and Neurotoxicology, Karolinska Institutet, Stockholm, Sweden.
    Shimizu, S.
    Laboratory of Molecular Genetics, Osaka University Medical School and Graduate School of Medicine, Osaka, Japan.
    Tsujimoto, Y.
    Laboratory of Molecular Genetics, Osaka University Medical School and Graduate School of Medicine, Osaka, Japan.
    Orrenius, S.
    Institute of Environmental Medicine, Division of Toxicology and Neurotoxicology, Karolinska Institutet, Stockholm, Sweden.
    Ceccatelli, C.
    Institute of Environmental Medicine, Division of Toxicology and Neurotoxicology, Karolinska Institutet, Stockholm, Sweden.
    Opening of plasma membrane voltage-dependent anion channels (VDAC) precedes caspase activation in neuronal apoptosis induced by toxic stimuli2005Inngår i: Cell Death and Differentiation, ISSN 1350-9047, E-ISSN 1476-5403, Vol. 12, nr 8, s. 1134-1140Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Apoptotic cell death is an essential process in the development of the central nervous system and in the pathogenesis of its degenerative diseases. Efflux of K+ and Cl- ions leads to the shrinkage of the apoptotic cell and facilitates the activation of caspases. Here, we present electrophysiological and immunocytochemical evidences for the activation of a voltage-dependent anion channel (VDAC) in the plasma membrane of neurons undergoing apoptosis. Anti-VDAC antibodies blocked the channel and inhibited the apoptotic process. In nonapoptotic cells, plasma membrane VDAC1 protein can function as a NADH (-ferricyanide) reductase. Opening of VDAC channels in apoptotic cells was associated with an increase in this activity, which was partly blocked by VDAC antibodies. Hence, it appears that there might be a dual role for this protein in the plasma membrane: (1) maintenance of redox homeostasis in normal cells and (2) promotion of anion efflux in apoptotic cells.

  • 24.
    Elinder, Fredrik
    et al.
    Karolinska Institute.
    Arhem, P
    Karolinska Institute.
    The functional surface charge density of a fast K channel in the myelinated axon of Xenopus laevis1998Inngår i: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 165, nr 2, s. 175-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The action of Mg2+ on the putative xKv1.1 channel in the myelinated axon of Xenopus laevis was analyzed in voltage clamp experiments. The main effect was a shift in positive direction of the open probability curve (16 mV at 20 mM Mg2+), calculated from measurements of the instantaneous current at Na reversal potential after 50-100 msec steps to different potentials. The shift was measured at an open probability level of 25% to separate it from shifts of other K channel populations in the nodal region. The results could be explained in terms of screening effects on fixed charges located on the surface of the channel protein. Using the Grahame equation the functional charge density was estimated to -0.45 e nm(-2). Analyzing this value, together with previously estimated values from other K channels, with reference to the charge of different extracellular loops of the channel protein, we conclude that the loop between the transmembrane S5 segment and the pore forming P segment determines the functional charge density of voltage-gated K channels.

  • 25.
    Elinder, Fredrik
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Börjesson, Sara I.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels2017Inngår i: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 8, artikkel-id 43Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (NaV), potassium (KV), calcium (CaV), and proton (HV) channels, as well as calcium-activated potassium (KCa), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.

  • 26.
    Elinder, Fredrik
    et al.
    Karolinska Institute.
    Liu, Y
    Karolinska Institute.
    Arhem, P
    Karolinska Institute.
    Divalent cation effects on the shaker K channel suggest a pentapeptide sequence as determinant of functional surface charge density1998Inngår i: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 165, nr 2, s. 183-189Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of the divalent cations strontium and magnesium on Shaker K channels expressed in Xenopus oocytes were investigated with a two-electrode voltage-clamp technique. 20 mM of the divalent cation shifted activation (conductance vs. potential), steady-state inactivation and inactivation time constant vs. potential curves 10-11 mV along the potential axis. The results were interpreted in terms of the surface charge theory, and the surface charge density was estimated to be -0.27 e nm(-2). A comparison of primary structure data and experimental data from the present and previous studies suggests that the first five residues on the extracellular loop between transmembrane segment 5 and the pore region constitutes the functional surface charges. The results further suggest that the surface charge density plays an important role in controlling the activation voltage range.

  • 27.
    Elinder, Fredrik
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Madeja, Michael
    University of Munster, Germany; Goethe University of Frankfurt, Germany.
    Zeberg, Hugo
    Karolinska Institute, Sweden.
    Arhem, Peter
    Karolinska Institute, Sweden.
    Extracellular Linkers Completely Transplant the Voltage Dependence from Kv1.2 Ion Channels to Kv2.12016Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 111, nr 8, s. 1679-1691Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transmembrane voltage needed to open different voltage-gated K (Kv) channels differs by up to 50 mV from each other. In this study we test the hypothesis that the channels voltage dependences to a large extent are set by charged amino-acid residues of the extracellular linkers of the Kv channels, which electrostatically affect the charged amino-acid residues of the voltage sensor S4. Extracellular cations shift the conductance-versus-voltage curve, G(V), by interfering with these extracellular charges. We have explored these issues by analyzing the effects of the divalent strontium ion (Sr2+) on the voltage dependence of the G(V) curves of wild-type and chimeric Kv channels expressed in Xenopus oocytes, using the voltage-clamp technique. Out of seven Kv channels, Kv1.2 was found to be most sensitive to Sr2+ (50 mM shifted G(V) by +21.7 mV), and Kv2.1 to be the least sensitive (+7.8 mV). Experiments on 25 chimeras, constructed from Kv1.2 and Kv2.1, showed that the large Sr2+-induced G(V) shift of Kv1.2 can be transferred to Kv2.1 by exchanging the extracellular linker between S3 and S4 (L3/4) in combination with either the extracellular linker between S5 and the pore (L5/P) or that between the pore and S6 (LP/6). The effects of the linker substitutions were nonadditive, suggesting specific structural interactions. The free energy of these interactions was similar to 20 kJ/mol, suggesting involvement of hydrophobic interactions and/or hydrogen bonds. Using principles from double-layer theory we derived an approximate linear equation (relating the voltage shifts to altered ionic strength), which proved to well match experimental data, suggesting that Sr2+ acts on these channels mainly by screening surface charges. Taken together, these results highlight the extracellular surface potential at the voltage sensor as an important determinant of the channels voltage dependence, making the extracellular linkers essential targets for evolutionary selection.

  • 28.
    Elinder, Fredrik
    et al.
    Linköpings universitet, Institutionen för biomedicin och kirurgi, Avdelningen för medicinsk cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Männikkö, Roope
    Pandey, Shilpi
    Larsson, H Peter
    Mode shifts in the voltage gating of the mouse and human HCN2 and HCN4 channels2006Inngår i: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 575, nr 2, s. 417-431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hyperpolarization-activated, cyclic-nucleotide-gated (HCN) channels regulate pacemaker activity in the heart and the brain. Previously, we showed that spHCN and HCN1 channels undergo mode shifts in their voltage dependences, shifting the conductance versus voltage curves by more than +50 mV when measured from a hyperpolarized potential compared to a depolarized potential. In addition, the kinetics of the ionic currents changed in parallel to these voltage shifts. In the studies reported here, we tested whether slower cardiac HCN channels also display similar mode shifts. We found that HCN2 and HCN4 channels expressed in oocytes from the frog Xenopus laevis do not display the activation kinetic changes that we observed in spHCN and HCN1. However, HCN2 and HCN4 channels display changes in their tail currents, suggesting that these channels also undergo mode shifts and that the conformational changes underlying the mode shifts are due to conserved aspects of HCN channels. With computer modelling, we show that in channels with relatively slow opening kinetics and fast mode-shift transitions, such as HCN2 and HCN4 channels, the mode shift effects are not readily observable, except in the tail kinetics. Computer simulations of sino-atrial node action potentials suggest that the HCN2 channel, together with the HCN1 channel, are important regulators of the heart firing frequency and that the mode shift is an important property to prevent arrhythmic firing. We conclude that although all HCN channels appear to undergo mode shifts -and thus may serve to prevent arrhythmic firing -it is mainly observable in ionic currents from HCN channels with faster kinetics. 2006 The Authors. Journal compilation © 2006 The Physiological Society.

  • 29.
    Elinder, Fredrik
    et al.
    Linköpings universitet, Institutionen för biomedicin och kirurgi, Cellbiologi. Linköpings universitet, Hälsouniversitetet. Karolinska Inst, Dept Neurosci, Nobel Inst Neurophysiol, Stockholm.
    Nilsson, J
    Karolinska Inst, Dept Neurosci, Nobel Inst Neurophysiol, Stockholm.
    Arhem, P
    Karolinska Inst, Dept Neurosci, Nobel Inst Neurophysiol, Stockholm.
    On the opening of voltage-gated ion channels2007Inngår i: Physiology and Behavior, ISSN 0031-9384, E-ISSN 1873-507X, Vol. 92, nr 1-2, s. 1-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels are key players in fast neuronal signalling Detailed knowledge about channel gating is essential for our understanding of channel function in general and of drug action of channels in particular. Despite a number of recent atomic channel structures, the opening of voltage-gated channels is the subject of heated debates. Here we will discuss two of the controversies: one concerning the mechanism of opening and closing the pore, and the other concerning the location and movement of the voltage sensor. The channels were originally suggested to open at a conserved proline rich sequence (PVP) at the intracellular end of the transmembrane segment 6 (S6). The crystallization of a channel in the open state instead suggested an opening involving a conserved glycine hinge located in the middle portion of S6. Based on pharmacological studies, autodocking and molecular dynamics simulations we have found support for the PVP-bend model. The voltage sensor, transmembrane segment 4 (S4), was originally suggested to be buried in the channel protein, undergoing a helical-screw-like motion to open the channel. A recent crystallographic study suggested that S4 is located in the periphery, facing lipid, and undergoing a paddle-like motion to open the channel We have found experimental evidence for a novel helical-screw model; with the voltage sensor moving in a screw-like fashion but being located in the periphery of the channel. This model opens up for understanding how lipophilic drugs and toxins directly affect the voltage sensor.

  • 30.
    Elinder, Fredrik
    et al.
    Karolinska Institute.
    Århem, P
    Karolinska Institute.
    Role of individual surface charges of voltage-gated K channels1999Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 77, nr 3, s. 1358-1362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fixed charges on the extracellular surface of voltage-gated ion channels influence the gating. In previous studies of cloned voltage-gated K channels, we found evidence that the functional surface charges are located on the peptide loop between the fifth transmembrane segment and the pore region (the S5-P loop). In the present study, we determine the role of individual charges of the S5-P loop by correlating primary structure with experimentally calculated surface potentials of the previously investigated channels. The results suggest that contributions to the surface potential at the voltage sensor of the different residues varies in an oscillating pattern, with the first residue of the N-terminal end of the S5-P loop, an absolutely conserved glutamate, contributing most. An analysis yields estimates of the distance between the residues and the voltage sensor, the first N-terminal residue being located at a distance of 5-6 Angstrom. To explain the results, a structural hypothesis, comprising an a-helical N-terminal end of the S5-P loop, is presented.

  • 31.
    Englund, Ulrika
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Inhibition of SCN2A ortholog upregulation in Xenopus laevis oocytes prevents cell death2014Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Transport of ions across the cell membrane is essential for the regulation of cell death and tissue homeostasis, and alterations in the function of voltage-gated ion channels and of the intracellular ionic compositions interfere with these processes. Opening of K, Na , or Cl channels have been linked to the apoptotic process and in many cases, opening of these channels precede caspase-3 activation and are thus early events in the apoptotic process. Consistent with the role of these channels in apoptosis, inhibition of these channels prevents or delays the apoptotic process. However, the role of ion channels during apoptosis has been difficult to explore, mainly due to unspecific/non-selective ion channe blockers. In the present investigation, the molecular identity of a  voltage-gated Na channel in oocytes from Xenopus laevis, which is crucial for the apoptotic response to mechanical stress, was identified. Specific down regulation of SCN2A Na channel expression by miRNA prevented apoptosis, suggesting that Na+ influx is essential for apoptosis in Xenopus oocytes.

  • 32.
    Englund, Ulrika
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Gertow, Jens
    Linköpings universitet, Institutionen för klinisk och experimentell medicin. Linköpings universitet, Hälsouniversitetet.
    Kågedal, Katarina
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    A Voltage Dependent Non-Inactivating Na+ Channel Activated during Apoptosis in Xenopus Oocytes2014Inngår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, nr 2, s. 0088381-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion channels in the plasma membrane are important for the apoptotic process. Different types of voltage-gated ion channels are up-regulated early in the apoptotic process and block of these channels prevents or delays apoptosis. In the present investigation we examined whether ion channels are up-regulated in oocytes from the frog Xenopus laevis during apoptosis. The two-electrode voltage-clamp technique was used to record endogenous ion currents in the oocytes. During staurosporine-induced apoptosis a voltage-dependent Na+ current increased three-fold. This current was activated at voltages more positive than 0 mV (midpoint of the open-probability curve was +55 mV) and showed almost no sign of inactivation during a 1-s pulse. The current was resistant to the Na+-channel blockers tetrodotoxin (1 mM) and amiloride (10 mM), while the Ca2+-channel blocker verapamil (50 mM) in the bath solution completely blocked the current. The intracellular Na+ concentration increased in staurosporine-treated oocytes, but could be prevented by replacing extracellular Na+ whith either K+ or Choline(+). Prevention of this influx of Na+ also prevented the STS-induced up-regulation of the caspase-3 activity, suggesting that the intracellular Na+ increase is required to induce apoptosis. Taken together, we have found that a voltage dependent Na+ channel is up-regulated during apoptosis and that influx of Na+ is a crucial step in the apoptotic process in Xenopus oocytes.

  • 33.
    Fulati, Alimujiang
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Usman Ali, Syed M.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Asif, Muhammad H.
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan. Pakistan.
    Hassan Alvi, Naveed Ul
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Willander, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska högskolan.
    Brännmark, Cecilia
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Strålfors, Peter
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Börjesson, Sara I.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Danielsson, Bengt
    Lund University, Sweden.
    An intracellular glucose biosensor based on nanoflake ZnO2010Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 150, nr 2, s. 673-680Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    In this study, an improved potentiometric intracellular glucose biosensor was fabricated with immobilization of glucose oxidase on a ZnO nanoporous material. The ZnO nanoporous material with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose sensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a linear glucosedependent electrochemical response over a wide range of glucose concentration (500 nM-10 mM). The measurements of intracellular glucose concentrations with our biosensor were consistent with the values of intracellular glucose concentrations reported in the literature. The sensor also demonstrated its capability by detecting an increase in the intracellular glucose concentration induced by insulin. We found that the ZnO nanoporous material provides sensitivity as high as 1.8 times higher than that obtained using ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the excellent performance of the developed nanosensor in sensitivity, stability, selectivity, reproducibility and anti-interference was achieved. All these advantageous features of this intracellular glucose biosensor based on functionalised ZnO nanoporous material compared to ZnO nanorods demonstrate a promising way of enhancing glucose biosensor performance to measure reliable intracellular glucose concentrations within single living cells.

  • 34.
    Henrion, Ulrike
    et al.
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi.
    Renhorn, Jakob
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Börjesson, Sara
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Nelson, Erin M
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Schwaiger, Christine S
    Royal Institute of Technology, Sweden .
    Bjelkmar, Par
    Royal Institute of Technology, Sweden Stockholm University, Sweden .
    Wallner, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Bioinformatik. Linköpings universitet, Tekniska högskolan.
    Lindahl, Erik
    Royal Institute of Technology, Sweden Stockholm University, Sweden .
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Tracking a complete voltage-sensor cycle with metal-ion bridges2012Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, nr 22, s. 8552-8557Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels open and close in response to changes in membrane potential, thereby enabling electrical signaling in excitable cells. The voltage sensitivity is conferred through four voltage-sensor domains (VSDs) where positively charged residues in the fourth transmembrane segment (S4) sense the potential. While an open state is known from the Kv1.2/2.1 X-ray structure, the conformational changes underlying voltage sensing have not been resolved. We present 20 additional interactions in one open and four different closed conformations based on metal-ion bridges between all four segments of the VSD in the voltage-gated Shaker K channel. A subset of the experimental constraints was used to generate Rosetta models of the conformations that were subjected to molecular simulation and tested against the remaining constraints. This achieves a detailed model of intermediate conformations during VSD gating. The results provide molecular insight into the transition, suggesting that S4 slides at least 12 angstrom along its axis to open the channel with a 3(10) helix region present that moves in sequence in S4 in order to occupy the same position in space opposite F290 from open through the three first closed states.

  • 35.
    Jakesova, Marie
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Silverå Ejneby, Malin
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Derek, Vedran
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Schmidt, Tony
    Med Univ Graz, Austria.
    Gryszel, Maciej
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Schindl, Rainer
    Med Univ Graz, Austria.
    Simon, Daniel
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Berggren, Magnus
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Glowacki, Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Laboratoriet för organisk elektronik. Linköpings universitet, Tekniska fakulteten.
    Optoelectronic control of single cells using organic photocapacitors2019Inngår i: Science Advances, E-ISSN 2375-2548, Vol. 5, nr 4, artikkel-id eaav5265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Optical control of the electrophysiology of single cells can be a powerful tool for biomedical research and technology. Here, we report organic electrolytic photocapacitors (OEPCs), devices that function as extracellular capacitive electrodes for stimulating cells. OEPCs consist of transparent conductor layers covered with a donor-acceptor bilayer of organic photoconductors. This device produces an open-circuit voltage in a physiological solution of 330 mV upon illumination using light in a tissue transparency window of 630 to 660 nm. We have performed electrophysiological recordings on Xenopus laevis oocytes, finding rapid (time constants, 50 mu s to 5 ms) photoinduced transient changes in the range of 20 to 110 mV. We measure photoinduced opening of potassium channels, conclusively proving that the OEPC effectively depolarizes the cell membrane. Our results demonstrate that the OEPC can be a versatile nongenetic technique for optical manipulation of electrophysiology and currently represents one of the simplest and most stable and efficient optical stimulation solutions.

  • 36.
    Johansson, Patrik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska högskolan.
    Jullesson, David
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska högskolan.
    Elfwing, Anders
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Liin, Sara
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Musumeci, Chiara
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Zeglio, Erica
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Solin, Niclas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Inganäs, Olle
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Electronic polymers in lipid membranes2015Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, nr 11242Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrical interfaces between biological cells and man-made electrical devices exist in many forms, but it remains a challenge to bridge the different mechanical and chemical environments of electronic conductors (metals, semiconductors) and biosystems. Here we demonstrate soft electrical interfaces, by integrating the metallic polymer PEDOT-S into lipid membranes. By preparing complexes between alkyl-ammonium salts and PEDOT-S we were able to integrate PEDOT-S into both liposomes and in lipid bilayers on solid surfaces. This is a step towards efficient electronic conduction within lipid membranes. We also demonstrate that the PEDOT-S@alkyl-ammonium: lipid hybrid structures created in this work affect ion channels in the membrane of Xenopus oocytes, which shows the possibility to access and control cell membrane structures with conductive polyelectrolytes.

  • 37.
    Keynes, RD
    et al.
    University of Cambridge.
    Elinder, Fredrik
    Karolinska Institute.
    Modelling the activation, opening, inactivation and reopening of the voltage-gated sodium channel1998Inngår i: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 265, nr 1393, s. 263-270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A model of the voltage-gated sodium channel is put forward suggesting that the four S4 voltage-sensors behave as screw-helices making a series of discrete transitions that carry one elementary charge for each notch of the screw helix. After the channel has been activated by the first two steps R reversible arrow P reversible arrow A in all four domains, followed by a voltage-independent rearrangement, it is opened by a third cooperative step A reversible arrow B in domains I, II and III in conjunction with hydration. Inactivation is a voltage-dependent process controlled by the third step A reversible arrow I in sensor IVS4, and the closing of the channel is brought about its dehydration. From the inactivated steady state the channel may be reopened by a fourth step, I reversible arrow C in sensor IVS4 and rehydration. The computed kinetics of the model are shown to conform closely with those observed experimentally.

  • 38.
    Keynes, RD
    et al.
    University of Cambridge.
    Elinder, Fredrik
    Karolinska Institute.
    On the slowly rising phase of the sodium gating current in the squid giant axon1998Inngår i: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 265, nr 1393, s. 255-262Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution records of the sodium gating current in the squid giant axon demonstrate the existence of a slowly rising phase that is first apparent at pulse potentials slightly below zero, and becomes increasingly pronounced at more positive potentials. At +80 mV the current reaches its peak with a delay of 30 mu s at 10 degrees C. It is suggested that this current is generated by the first two steps labelled R--greater thanP and P--greater thanA in the S4 units of all four domains of the series-parallel gating system, activating the channel before its opening by the third steps A--greater thanB in domains I, II and III in conjunction with hydration. The kinetics of the slowly rising phase can only be explained by the incorporation of an appropriate degree of voltage-dependent cooperativity between the S4 voltage-sensors for their two initial transitions.

  • 39.
    Keynes, RD
    et al.
    University of Cambridge.
    Elinder, Fredrik
    Karolinska Institute.
    The screw-helical voltage gating of ion channels1999Inngår i: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 266, nr 1421, s. 843-852Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the voltage-gated ion channels of every animal, whether they are selective for K+, Na+ or Ca2+, the voltage sensors are the S4 transmembrane segments carrying four to eight positive charges always separated by two uncharged residues. It is proposed that they move across the membrane in a screw-helical fashion in a series of three or more steps that each transfer a single electronic charge. The unit steps are stabilized by ion pairing between the mobile positive charges and fixed negative charges, of which there are invariably two located near the inner ends of segments S2 and S3 and a third near the outer end of either S2 or S3. Opening of the channel involves three such steps in each domain.

  • 40.
    Klement, G.
    et al.
    Nobel Institute for Neurophysiology, Dept. of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
    Nilsson, J.
    Nobel Institute for Neurophysiology, Dept. of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
    Arhem, P.
    Århem, P., Nobel Institute for Neurophysiology, Dept. of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    A tyrosine substitution in the cavity wall of a K channel induces an inverted inactivation2008Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 94, nr 8, s. 3014-3022Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K+ ion. In the cardiac human ether-a-go-go-related gene channel, which exhibits slow activation and fast inactivation, the corresponding residue is tyrosine. To explore the role of a tyrosine at this position in the Shaker channel, we studied I470Y. The activation became slower, and the inactivation faster and more complex. At +60 mV the channel inactivated with two distinct rates (t1 = 20 ms, t2 = 400 ms). Experiments with tetraethylammonium and high K + concentrations suggest that the slower component was of the P/C-type. In addition, an inactivation component with inverted voltage dependence was introduced. A step to -40 mV inactivates the channel with a time constant of 500 ms. Negative voltage steps do not cause the channel to recover from this inactivated state (t » 10 min), whereas positive voltage steps quickly do (t = 2 ms at +60 mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state. © 2008 by the Biophysical Society.

  • 41.
    Larsson, HP
    et al.
    Karolinska Institute.
    Elinder, Fredrik
    Karolinska Institute.
    A conserved glutamate is important for slow inactivation in K+ channels2000Inngår i: Neuron, ISSN 0896-6273, E-ISSN 1097-4199, Vol. 27, nr 3, s. 573-583Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels undergo slow inactivation during prolonged depolarizations. We investigated the role of a conserved glutamate at the extracellular end of segment 5 (S5) in slow inactivation by mutating it to a cysteine (E418C in Shaker). We could lock the channel in two different conformations by disulfide-linking 418C to two different cysteines, introduced in the Pore-S6 (P-S6) loop. Our results suggest that E418 is normally stabilizing the open conformation of the slow inactivation gate by forming hydrogen bonds with the P-S6 loop. Breaking these bonds allows the P-S6 loop to rotate, which closes the slow inactivation gate. Our results also suggest a mechanism of how the movement of the voltage sensor can induce slow inactivation by destabilizing these bonds.

  • 42.
    Liin, Sara
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Karlsson, Urban
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Bentzen, B. H.
    University of Copenhagen, Denmark.
    Schmitt, N.
    University of Copenhagen, Denmark.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Polyunsaturated fatty acids are potent openers of human M-channels expressed in Xenopus laevis oocytes2016Inngår i: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 218, nr 1, s. 28-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aim: Polyunsaturated fatty acids have been reported to reduce neuronal excitability, in part by promoting inactivation of voltage-gated sodium and calcium channels. Effects on neuronal potassium channels are less explored and experimental data ambiguous. The aim of this study was to investigate anti-excitable effects of polyunsaturated fatty acids on the neuronal M-channel, important for setting the resting membrane potential in hippocampal and dorsal root ganglion neurones. Methods: Effects of fatty acids and fatty acid analogues on mouse dorsal root ganglion neurones and on the human KV7.2/3 channel expressed in Xenopus laevis oocytes were studied using electrophysiology. Results: Extracellular application of physiologically relevant concentrations of the polyunsaturated fatty acid docosahexaenoic acid hyperpolarized the resting membrane potential (-2.4 mV by 30 mu M) and increased the threshold current to evoke action potentials in dorsal root ganglion neurones. The polyunsaturated fatty acids docosahexaenoic acid, alpha-linolenic acid and eicosapentaenoic acid facilitated opening of the human M-channel, comprised of the heteromeric human KV7.2/3 channel expressed in Xenopus oocytes, by shifting the conductance-vs.-voltage curve towards more negative voltages (by -7.4 to -11.3 mV by 70 mu M). Uncharged docosahexaenoic acid methyl ester and monounsaturated oleic acid did not facilitate opening of the human KV7.2/3 channel. Conclusions: These findings suggest that circulating polyunsaturated fatty acids, with a minimum requirement of multiple double bonds and a charged carboxyl group, dampen excitability by opening neuronal M-channels. Collectively, our data bring light to the molecular targets of polyunsaturated fatty acids and thus a possible mechanism by which polyunsaturated fatty acids reduce neuronal excitability.

  • 43.
    Liin, Sara
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Lund, Per-Eric
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Larsson, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Brask, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Wallner, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Bioinformatik. Linköpings universitet, Tekniska fakulteten.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelning för neurobiologi. Linköpings universitet, Medicinska fakulteten.
    Biaryl sulfonamide motifs up- or down-regulate ion channel activity by activating voltage sensors2018Inngår i: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 150, nr 8, s. 1215-1230Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated ion channels are key molecules for the generation of cellular electrical excitability. Many pharmaceutical drugs target these channels by blocking their ion-conducting pore, but in many cases, channel-opening compounds would be more beneficial. Here, to search for new channel-opening compounds, we screen 18,000 compounds with high-throughput patch-clamp technology and find several potassium-channel openers that share a distinct biaryl-sulfonamide motif. Our data suggest that the negatively charged variants of these compounds bind to the top of the voltage-sensor domain, between transmembrane segments 3 and 4, to open the channel. Although we show here that biaryl-sulfonamide compounds open a potassium channel, they have also been reported to block sodium and calcium channels. However, because they inactivate voltage-gated sodium channels by promoting activation of one voltage sensor, we suggest that, despite different effects on the channel gates, the biaryl-sulfonamide motif is a general ion-channel activator motif. Because these compounds block action potential-generating sodium and calcium channels and open an action potential-dampening potassium channel, they should have a high propensity to reduce excitability. This opens up the possibility to build new excitability-reducing pharmaceutical drugs from the biaryl-sulfonamide scaffold.

  • 44.
    Liin, Sara
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten. University of Miami, FL 33136 USA.
    Silverå Ejneby, Malin
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Barro-Soria, Rene
    University of Miami, FL 33136 USA.
    Alexander Skarsfeldt, Mark
    University of Copenhagen, Denmark; University of Copenhagen, Denmark.
    Larsson, Johan
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten. University of Miami, FL 33136 USA.
    Starck Härlin, Frida
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten. University of Miami, FL 33136 USA.
    Parkkari, Teija
    University of Eastern Finland, Finland.
    Hjorth Bentzen, Bo
    University of Copenhagen, Denmark; University of Copenhagen, Denmark.
    Schmitt, Nicole
    University of Copenhagen, Denmark; University of Copenhagen, Denmark.
    Peter Larsson, H.
    University of Miami, FL 33136 USA.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Polyunsaturated fatty acid analogs act antiarrhythmically on the cardiac I-Ks channel2015Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, nr 18, s. 5714-5719Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polyunsaturated fatty acids (PUFAs) affect cardiac excitability. Kv7.1 and the beta-subunit KCNE1 form the cardiac I-Ks channel that is central for cardiac repolarization. In this study, we explore the prospects of PUFAs as I-Ks channel modulators. We report that PUFAs open Kv7.1 via an electrostatic mechanism. Both the polyunsaturated acyl tail and the negatively charged carboxyl head group are required for PUFAs to open Kv7.1. We further show that KCNE1 coexpression abolishes the PUFA effect on Kv7.1 by promoting PUFA protonation. PUFA analogs with a decreased pK(a) value, to preserve their negative charge at neutral pH, restore the sensitivity to open I-Ks channels. PUFA analogs with a positively charged head group inhibit I-Ks channels. These different PUFA analogs could be developed into drugs to treat cardiac arrhythmias. In support of this possibility, we show that PUFA analogs act antiarrhythmically in embryonic rat cardiomyocytes and in isolated perfused hearts from guinea pig.

  • 45.
    Lundengård, Karin
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Cedersund, Gunnar
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Engström, Maria
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Mechanistic Modelling Investigates the Neural Basis behind the Hemodynamic Response in fMRI2015Inngår i: 16TH NORDIC-BALTIC CONFERENCE ON BIOMEDICAL ENGINEERING, Springer Science Business Media , 2015, Vol. 48, s. 86-87Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This work serves as a basis for a new type of fMRI analysis, which is based on a mechanistic interpretation of the hemodynamic response to synaptic activity. Activation was measured in the visual cortex of 12 healthy controls and ordinary differential equation models were fitted to the time series of the hemodynamic response. This allowed us to reject or refine previously proposed mechanistic hypotheses. This is the first attempt to describe the hemodynamic response quantitatively based on recent neurobiological findings. This mechanistic approach stands in contrast to the standard phenomenological description using the gamma variate function.

  • 46.
    Lundengård, Karin
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Cedersund, Gunnar
    Linköpings universitet, Institutionen för medicinsk teknik. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi.
    Sten, Sebastian
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Leong, Felix
    Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Medicinska fakulteten.
    Smedberg, Alexander
    Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Medicinska fakulteten.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Engström, Maria
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Mechanistic Mathematical Modeling Tests Hypotheses of the Neurovascular Coupling in fMRI2016Inngår i: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 12, nr 6, artikkel-id e1004971Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Functional magnetic resonance imaging (fMRI) measures brain activity by detecting the blood-oxygen-level dependent (BOLD) response to neural activity. The BOLD response depends on the neurovascular coupling, which connects cerebral blood flow, cerebral blood volume, and deoxyhemoglobin level to neuronal activity. The exact mechanisms behind this neurovascular coupling are not yet fully investigated. There are at least three different ways in which these mechanisms are being discussed. Firstly, mathematical models involving the so-called Balloon model describes the relation between oxygen metabolism, cerebral blood volume, and cerebral blood flow. However, the Balloon model does not describe cellular and biochemical mechanisms. Secondly, the metabolic feedback hypothesis, which is based on experimental findings on metabolism associated with brain activation, and thirdly, the neurotransmitter feed-forward hypothesis which describes intracellular pathways leading to vasoactive substance release. Both the metabolic feedback and the neurotransmitter feed-forward hypotheses have been extensively studied, but only experimentally. These two hypotheses have never been implemented as mathematical models. Here we investigate these two hypotheses by mechanistic mathematical modeling using a systems biology approach; these methods have been used in biological research for many years but never been applied to the BOLD response in fMRI. In the current work, model structures describing the metabolic feedback and the neurotransmitter feed-forward hypotheses were applied to measured BOLD responses in the visual cortex of 12 healthy volunteers. Evaluating each hypothesis separately shows that neither hypothesis alone can describe the data in a biologically plausible way. However, by adding metabolism to the neurotransmitter feed-forward model structure, we obtained a new model structure which is able to fit the estimation data and successfully predict new, independent validation data. These results open the door to a new type of fMRI analysis that more accurately reflects the true neuronal activity.

  • 47.
    Lundengård, Karin
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Engström, Maria
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    A mechanistic model for blood flow regulation in response to neuronal activity2013Konferansepaper (Annet vitenskapelig)
  • 48.
    Männikkö, Roope
    et al.
    Karolinska Institutet.
    Pandey, Shilpi
    Oregon Health and Science University.
    Larsson, H Peter
    Oregon Health and Science University.
    Elinder, Fredrik
    Karolinska Institutet.
    Hysteresis in the voltage dependence of HCN channels: Conversion between two modes affects pacemaker properties2005Inngår i: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 125, s. 305-326Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels are important for rhythmic activity in the brain and in the heart. In this study, using ionic and gating current measurements, we show that cloned spHCN channels undergo a hysteresis in their voltage dependence during normal gating. For example, both the gating charge versus voltage curve, Q(V), and the conductance versus voltage curve, G(V), are shifted by about +60 mV when measured from a hyperpolarized holding potential compared with a depolarized holding potential. In addition, the kinetics of the tail current and the activation current change in parallel to the voltage shifts of the Q(V) and G(V) curves. Mammalian HCN1 channels display similar effects in their ionic currents, suggesting that the mammalian HCN channels also undergo voltage hysteresis. We propose a model in which HCN channels transit between two modes. The voltage dependence in the two modes is shifted relative to each other, and the occupancy of the two modes depends on the previous activation of the channel. The shifts in the voltage dependence are fast (τ ≈ 100 ms) and are not accompanied by any apparent inactivation. In HCN1 channels, the shift in voltage dependence is slower in a 100 mM K extracellular solution compared with a 1 mM K solution. Based on these findings, we suggest that molecular conformations similar to slow (C-type) inactivation of K channels underlie voltage hysteresis in HCN channels. The voltage hysteresis results in HCN channels displaying different voltage dependences during different phases in the pacemaker cycle. Computer simulations suggest that voltage hysteresis in HCN channels decreases the risk of arrhythmia in pacemaker cells.

  • 49.
    Nilsson, J
    et al.
    Karolinska Institute.
    Elinder, Fredrik
    Karolinska Institute.
    Arhem, P
    Karolinska Institute.
    Mechanisms of bupivacaine action on Na+ and K+ channels in myelinated axons of Xenopus laevis1998Inngår i: European Journal of Pharmacology, ISSN 0014-2999, E-ISSN 1879-0712, Vol. 360, nr 1, s. 21-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The local anaesthetic bupivacaine has recently been proposed to inhibit Na+ channels indirectly by making the resting potential less negative. To test this hypothesis we analysed the effects of bupivacaine on voltage and current clamped nodes of Ranvier. Contrary to the hypothesis, the leak current and the resting potential were unaffected. The Na+ and K+ channels were, however, affected at relatively low concentrations (33 mu M). Steady-state activation curves were decreased without notable shift effects, whereas the Naf inactivation curve was decreased and shifted in negative direction. The effect on the Na+ current was tentatively explained by a single-site, state-dependent binding model (K-d = 44 mu M), while that on the K+ current was explained by two population-specific mechanisms, one open-state dependent (K-d = 550 mu M) and one state independent (K-d = 59 mu M). The binding stoichiometry was higher than 1:1 for the main sites of action. In conclusion, bupivacaine exerts its main anaesthetic action on myelinated nerve axons by a direct modification of Na+ channels.

  • 50.
    Nilsson, Johanna
    et al.
    Karolinska Institute.
    Madeja, Michael
    University of Munster, Germany.
    Elinder, Fredrik
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Arhem, Peter
    Karolinska Institute.
    Bupivacaine Blocks N-Type Inactivating K-v Channels in the Open State: No Allosteric Effect on Inactivation Kinetics2008Inngår i: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 95, nr 11, s. 5138-5152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local anesthetics bind to ion channels in a state-dependent manner. For noninactivating voltage-gated K channels the binding mainly occurs in the open state, while for voltage-gated inactivating Na channels it is assumed to occur mainly in inactivated states, leading to an allosterically caused increase in the inactivation probability, reflected in a negative shift of the steady-state inactivation curve, prolonged recovery from inactivation, and a frequency-dependent block. How local anesthetics bind to N-type inactivating K channels is less explored. In this study, we have compared bupivacaine effects on inactivating (Shaker and K(v)3.4) and noninactivating (Shaker-IR and K(v)3.2) channels, expressed in Xenopus oocytes. Bupivacaine was found to block these channels time-dependently without shifting the steady-state inactivation curve markedly, without a prolonged recovery from inactivation, and without a frequency-dependent block. An analysis, including computational testing of kinetic models, suggests binding to the channel mainly in the open state, with affinities close to those estimated for corresponding noninactivating channels (300 and 280 mu M for Shaker and Shaker-IR, and 60 and 90 mu M for K(v)3.4 and K(v)3.2). The similar magnitudes of K-d, as well as of blocking and unblocking rate constants for inactivating and noninactivating Shaker channels, most likely exclude allosteric interactions between the inactivation mechanism and the binding site. The relevance of these results for understanding the action of local anesthetics on Na channels is discussed.

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