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Pantazis, Antonios
Publications (10 of 10) Show all publications
Pantazis, A. & Olcese, R. (2019). Cut-Open Oocyte Voltage-Clamp Technique (Living Editioned.). In: Gordon Roberts, Anthony Watts, European Biophysical Societies (Ed.), Encyclopedia of Biophysics: . Berlin, Heidelberg: Springer Berlin/Heidelberg
Open this publication in new window or tab >>Cut-Open Oocyte Voltage-Clamp Technique
2019 (English)In: Encyclopedia of Biophysics / [ed] Gordon Roberts, Anthony Watts, European Biophysical Societies, Berlin, Heidelberg: Springer Berlin/Heidelberg, 2019, Living EditionChapter in book (Refereed)
Abstract [en]

The cut-open oocyte Vaseline gap (COVG) voltage clamp technique, a relatively recent addition to the electrophysiologist’s armamentarium, was specifically developed by Drs. Stefani and Bezanilla (Bezanilla et al. 1991) to achieve low-noise recordings of the membrane of Xenopus laevis oocytes with fast clamp speed and thus optimize the most popular transient expression system to reveal the activity voltage-dependent proteins previously difficult to resolve by alternative methods. The high degree of specialization of this technique is complemented by its flexibility; in addition to oocyte perfusion, COVG can be combined with optical measurements (voltage clamp fluorometry and spectroscopy) and flash photolysis for the instantaneous release of intracellular caged compounds, expanding its use beyond electrophysiology.

Place, publisher, year, edition, pages
Berlin, Heidelberg: Springer Berlin/Heidelberg, 2019 Edition: Living Edition
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Neurosciences
Identifiers
urn:nbn:se:liu:diva-162793 (URN)10.1007/978-3-642-35943-9_371-1 (DOI)9783642359439 (ISBN)
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-19Bibliographically approved
Venugopal, S., Seki, S., Terman, D. H., Pantazis, A., Olcese, R., Wiedau-Pazos, M. & Chandler, S. H. (2019). Resurgent Na+ Current Offers Noise Modulation in Bursting Neurons.. PloS Computational Biology, 15(6), Article ID e1007154.
Open this publication in new window or tab >>Resurgent Na+ Current Offers Noise Modulation in Bursting Neurons.
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2019 (English)In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 15, no 6, article id e1007154Article in journal (Refereed) Published
Abstract [en]

Neurons utilize bursts of action potentials as an efficient and reliable way to encode information. It is likely that the intrinsic membrane properties of neurons involved in burst generation may also participate in preserving its temporal features. Here we examined the contribution of the persistent and resurgent components of voltage-gated Na+ currents in modulating the burst discharge in sensory neurons. Using mathematical modeling, theory and dynamic-clamp electrophysiology, we show that, distinct from the persistent Na+ component which is important for membrane resonance and burst generation, the resurgent Na+ can help stabilize burst timing features including the duration and intervals. Moreover, such a physiological role for the resurgent Na+ offered noise tolerance and preserved the regularity of burst patterns. Model analysis further predicted a negative feedback loop between the persistent and resurgent gating variables which mediate such gain in burst stability. These results highlight a novel role for the voltage-gated resurgent Na+ component in moderating the entropy of burst-encoded neural information.

Place, publisher, year, edition, pages
PLOS, 2019
National Category
Bioinformatics (Computational Biology) Neurosciences
Identifiers
urn:nbn:se:liu:diva-162286 (URN)10.1371/journal.pcbi.1007154 (DOI)
Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2019-12-17Bibliographically approved
Pantazis, A. (2013). Cut-open Oocyte Voltage Clamp Technique (1ed.). In: Gordon C K Roberts (Ed.), Encyclopedia of Biophysics: (pp. 406-413). Springer Berlin/Heidelberg
Open this publication in new window or tab >>Cut-open Oocyte Voltage Clamp Technique
2013 (English)In: Encyclopedia of Biophysics / [ed] Gordon C K Roberts, Springer Berlin/Heidelberg, 2013, 1, p. 406-413Chapter in book (Other academic)
Abstract [en]

The cut-open oocyte Vaseline gap (COVG) voltage-clamp technique, a relatively recent addition to theelectrophysiologist’s armamentarium, was specificallydeveloped by Drs. Stefani and Bezanilla (Bezanillaet al.1991) to achieve low-noise recordings of themembrane ofXenopus laevisoocytes with fast clampspeed and, thus, optimize the most popular transientexpression system to reveal the activity voltage-dependent proteins previously difficult to resolve byalternative methods. The high degree of specializationof this technique is complemented by its flexibility: inaddition  to  oocyte  perfusion,  COVG  can  beencombined  with  optical  measurements  (voltage-clamp fluorometry and spectroscopy) and flash pho-tolysisfor the instantaneous release of intracellular-caged  compounds,  expanding  its  use  beyondelectrophysiology.

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2013 Edition: 1
National Category
Biophysics Neurosciences
Identifiers
urn:nbn:se:liu:diva-162180 (URN)9783642167119 (ISBN)9783642167133 (ISBN)9783642167126 (ISBN)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-26Bibliographically approved
Hoshi, T., Pantazis, A. & Olcese, R. (2013). Transduction of Voltage and Ca2+ Signals by Slo1 BK Channels. Physiology (Bethesda), 28(3), 172-189
Open this publication in new window or tab >>Transduction of Voltage and Ca2+ Signals by Slo1 BK Channels
2013 (English)In: Physiology (Bethesda), ISSN 1548-9213, Vol. 28, no 3, p. 172-189Article, review/survey (Refereed) Published
Abstract [en]

Large-conductance Ca2+- and voltage-gated K+ channels are activated by an increase in intracellular Ca2+ concentration and/or depolarization. The channel activation mechanism is well described by an allosteric model encompassing the gate, voltage sensors, and Ca2+ sensors, and the model is an excellent framework to understand the influences of auxiliary β and γ subunits and regulatory factors such as Mg2+. Recent advances permit elucidation of structural correlates of the biophysical mechanism.

Place, publisher, year, edition, pages
Amercian Physiolocial Society, 2013
National Category
Biophysics
Identifiers
urn:nbn:se:liu:diva-162181 (URN)10.1152/physiol.00055.2012 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-26Bibliographically approved
Savalli, N., Pantazis, A., Yusifov, T., Sigg, D. & Olcese, R. (2012). The contribution of RCK domains to human BK channel allosteric activation. Journal of Biological Chemistry, 287(26), 21741-21750
Open this publication in new window or tab >>The contribution of RCK domains to human BK channel allosteric activation
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2012 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 287, no 26, p. 21741-21750Article in journal (Refereed) Published
Abstract [en]

Large conductance voltage- and Ca2+-activated K+ (BK) channels are potent regulators of cellular processes including neuronal firing, synaptic transmission, cochlear hair cell tuning, insulin release, and smooth muscle tone. Their unique activation pathway relies on structurally distinct regulatory domains including one transmembrane voltage-sensing domain (VSD) and two intracellular high affinity Ca2+-sensing sites per subunit (located in the RCK1 and RCK2 domains). Four pairs of RCK1 and RCK2 domains form a Ca2+-sensing apparatus known as the “gating ring.” The allosteric interplay between voltage- and Ca2+-sensing apparati is a fundamental mechanism of BK channel function. Using voltage-clamp fluorometry and UV photolysis of intracellular caged Ca2+, we optically resolved VSD activation prompted by Ca2+ binding to the gating ring. The sudden increase of intracellular Ca2+ concentration ([Ca2+]i) induced a hyperpolarizing shift in the voltage dependence of both channel opening and VSD activation, reported by a fluorophore labeling position 202, located in the upper side of the S4 transmembrane segment. The neutralization of the Ca2+ sensor located in the RCK2 domain abolished the effect of [Ca2+]i increase on the VSD rearrangements. On the other hand, the mutation of RCK1 residues involved in Ca2+ sensing did not prevent the effect of Ca2+ release on the VSD, revealing a functionally distinct interaction between RCK1 and RCK2 and the VSD. A statistical-mechanical model quantifies the complex thermodynamics interplay between Ca2+ association in two distinct sites, voltage sensor activation, and BK channel opening.

Place, publisher, year, edition, pages
American Society for Biochemistry and Molecular Biology, 2012
National Category
Biophysics
Identifiers
urn:nbn:se:liu:diva-162178 (URN)10.1074/jbc.M112.346171 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-26Bibliographically approved
Madhvani, R. V., Xie, Y., Pantazis, A., Garfinkel, A., Qu, Z. & Weiss, J. N. (2011). Shaping a New Ca2+ Conductance to Suppress Early Afterdepolarizations in Cardiac Myocytes. Journal of Physiology, 589(24), 6081-6092
Open this publication in new window or tab >>Shaping a New Ca2+ Conductance to Suppress Early Afterdepolarizations in Cardiac Myocytes
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2011 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 589, no 24, p. 6081-6092Article in journal (Refereed) Published
Abstract [en]

Non‐technical summary Diseases, genetic defects, or ionic imbalances can alter the normal electrical activity of cardiac myocytes causing an anomalous heart rhythm, which can degenerate to ventricular fibrillation (VF) and sudden cardiac death. Well‐recognized triggers for VF are aberrations of the cardiac action potential, known as early afterdepolarizations (EADs). In this study, combining mathematical modelling and experimental electrophysiology in real‐time (dynamic clamp), we investigated the dependence of EADs on the biophysical properties of the L‐type Ca2+ current (ICa,L) and identified modifications of ICa,L properties which effectively suppress EAD. We found that minimal changes in the voltage dependence of activation or inactivation of ICa,L can dramatically reduce the occurrence of EADs in cardiac myocytes exposed to different EAD‐inducing conditions. This work assigns a critical role to the L‐type Ca2+ channel biophysical properties for EADs formation and identifies the L‐type Ca2+ channel as a promising therapeutic target to suppress EADs and their arrhythmogenic effects.

Place, publisher, year, edition, pages
John Wiley & Sons, 2011
National Category
Biophysics
Identifiers
urn:nbn:se:liu:diva-162177 (URN)10.1113/jphysiol.2011.219600 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-26Bibliographically approved
Pantazis, A., Kohanteb, A. P. & Olcese, R. (2010). Relative Motion of Transmembrane Segments S0 and S4 during Voltage Sensor Activation in the Human BKCa Channel. The Journal of General Physiology, 136(6), 645-657
Open this publication in new window or tab >>Relative Motion of Transmembrane Segments S0 and S4 during Voltage Sensor Activation in the Human BKCa Channel
2010 (English)In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 136, no 6, p. 645-657Article in journal (Refereed) Published
Abstract [en]

Large-conductance voltage- and Ca2+-activated K+ (BKCa) channel α subunits possess a unique transmembrane helix referred to as S0 at their N terminus, which is absent in other members of the voltage-gated channel superfamily. Recently, S0 was found to pack close to transmembrane segments S3 and S4, which are important components of the BKCa voltage-sensing apparatus. To assess the role of S0 in voltage sensitivity, we optically tracked protein conformational rearrangements from its extracellular flank by site-specific labeling with an environment-sensitive fluorophore, tetramethylrhodamine maleimide (TMRM). The structural transitions resolved from the S0 region exhibited voltage dependence similar to that of charge-bearing transmembrane domains S2 and S4. The molecular determinant of the fluorescence changes was identified in W203 at the extracellular tip of S4: at hyperpolarized potential, W203 quenches the fluorescence of TMRM labeling positions at the N-terminal flank of S0. We provide evidence that upon depolarization, W203 (in S4) moves away from the extracellular region of S0, lifting its quenching effect on TMRM fluorescence. We suggest that S0 acts as a pivot component against which the voltage-sensitive S4 moves upon depolarization to facilitate channel activation.

Place, publisher, year, edition, pages
Rockefeller University Press, 2010
National Category
Biophysics
Identifiers
urn:nbn:se:liu:diva-162175 (URN)10.1085/jgp.201010503 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2020-03-11Bibliographically approved
Yusifov, T., Javaherian, A. D., Pantazis, A., Gandhi, C. S. & Olcese, O. (2010). The RCK1 Domain of the Human BKCa Channel Transduces Ca2+ Binding into Structural Rearrangements. The Journal of General Physiology, 136(2), 189-202
Open this publication in new window or tab >>The RCK1 Domain of the Human BKCa Channel Transduces Ca2+ Binding into Structural Rearrangements
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2010 (English)In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 136, no 2, p. 189-202Article in journal (Refereed) Published
Abstract [en]

Large-conductance voltage- and Ca2+-activated K+ (BKCa) channels play a fundamental role in cellular function by integrating information from their voltage and Ca2+ sensors to control membrane potential and Ca2+ homeostasis. The molecular mechanism of Ca2+-dependent regulation of BKCa channels is unknown, but likely relies on the operation of two cytosolic domains, regulator of K+ conductance (RCK)1 and RCK2. Using solution-based investigations, we demonstrate that the purified BKCa RCK1 domain adopts an α/β fold, binds Ca2+, and assembles into an octameric superstructure similar to prokaryotic RCK domains. Results from steady-state and time-resolved spectroscopy reveal Ca2+-induced conformational changes in physiologically relevant [Ca2+]. The neutralization of residues known to be involved in high-affinity Ca2+ sensing (D362 and D367) prevented Ca2+-induced structural transitions in RCK1 but did not abolish Ca2+ binding. We provide evidence that the RCK1 domain is a high-affinity Ca2+ sensor that transduces Ca2+ binding into structural rearrangements, likely representing elementary steps in the Ca2+-dependent activation of human BKCa channels.

Place, publisher, year, edition, pages
Rockefeller University Press, 2010
National Category
Structural Biology
Identifiers
urn:nbn:se:liu:diva-162174 (URN)10.1085/jgp.200910374 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2020-03-10Bibliographically approved
Pantazis, A., Segaran, A., Liu, C.-H., Nikolaev, A., Rister, J., Thum, A. S., . . . Hardie, R. C. (2008). Distinct Roles for Two Histamine Receptors (hclA and hclB) at the Drosophila Photoreceptor Synapse. Journal of Neuroscience, 28(29), 7250-7259
Open this publication in new window or tab >>Distinct Roles for Two Histamine Receptors (hclA and hclB) at the Drosophila Photoreceptor Synapse
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2008 (English)In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 28, no 29, p. 7250-7259Article in journal (Refereed) Published
Abstract [en]

Histamine (HA) is the photoreceptor neurotransmitter in arthropods, directly gating chloride channels on large monopolar cells (LMCs), postsynaptic to photoreceptors in the lamina. Two histamine-gated channel genes that could contribute to this channel in Drosophila are hclA (also known as ort) and hclB (also known as hisCl1), both encoding novel members of the Cys-loop receptor superfamily. Drosophila S2 cells transfected with these genes expressed both homomeric and heteromeric histamine-gated chloride channels. The electrophysiological properties of these channels were compared with those from isolated Drosophila LMCs. HCLA homomers had nearly identical HA sensitivity to the native receptors (EC50 = 25 ÎŒm). Single-channel analysis revealed further close similarity in terms of single-channel kinetics and subconductance states (~25, 40, and 60 pS, the latter strongly voltage dependent). In contrast, HCLB homomers and heteromeric receptors were more sensitive to HA (EC50 = 14 and 1.2 ÎŒm, respectively), with much smaller single-channel conductances (~4 pS). Null mutations of hclA (ortUS6096) abolished the synaptic transients in the electroretinograms (ERGs). Surprisingly, the ERG “on” transients in hclB mutants transients were approximately twofold enhanced, whereas intracellular recordings from their LMCs revealed altered responses with slower kinetics. However, HCLB expression within the lamina, assessed by both a GFP (green fluorescent protein) reporter gene strategy and mRNA tagging, was exclusively localized to the glia cells, whereas HCLA expression was confirmed in the LMCs. Our results suggest that the native receptor at the LMC synapse is an HCLA homomer, whereas HCLB signaling via the lamina glia plays a previously unrecognized role in shaping the LMC postsynaptic response.

Place, publisher, year, edition, pages
Society for Neuroscience, 2008
National Category
Neurosciences
Identifiers
urn:nbn:se:liu:diva-162197 (URN)10.1523/JNEUROSCI.1654-08.2008 (DOI)
Available from: 2019-11-22 Created: 2019-11-22 Last updated: 2019-11-26Bibliographically approved
Pantazis, A., Keegan, P., Postma, M. & Schwiening, C. J. (2006). The Effect of Neuronal Morphology and Membrane-permeant Weak Acid and Base on the Dissipation of Depolarization-induced pH Gradients in Snail Neurons. Pflügers Archiv: European Journal of Physiology, 452(2), 175-187
Open this publication in new window or tab >>The Effect of Neuronal Morphology and Membrane-permeant Weak Acid and Base on the Dissipation of Depolarization-induced pH Gradients in Snail Neurons
2006 (English)In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 452, no 2, p. 175-187Article in journal (Refereed) Published
Abstract [en]

Neuronal depolarization causes larger intracellular pH (pHi) shifts in axonal and dendritic regions than in the cell body. In this paper, we present evidence relating the time for collapse of these gradients to neuronal morphology. We have used ratiometric pHi measurements using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) in whole-cell patch-clamped snail neurons to study the collapse of longitudinal pH gradients. Using depolarization to open voltage-gated proton channels, we produced alkaline pHi microdomains. In the absence of added mobile buffers, facilitated H+ diffusion down the length of the axon plays a critical role in determining pHi microdomain lifetime, with axons of ∼100 μm allowing pH differences to be maintained for >60 s. An application of mobile, membrane-permeant pH buffers accelerated the collapse of the alkaline-pH gradients but, even at 30 mM, was unable to abolish them. Modeling of the pHi dynamics showed that both the relatively weak effect of the weak acid/base on the peak size of the pH gradient and the accelerated collapse of the pH gradient could be due to the time taken for equilibration of the weak acid and base across the cell. We propose that appropriate weak acid/base mixes may provide a simple method for studying the role of local pHi signals without perturbing steady-state pHi. Furthermore, an extrapolation of our in vitro data to longer and thinner neuronal structures found in the mammalian nervous system suggests that dendritic and axonal pHi are likely to be dominated by local pHi-regulating mechanisms rather than simply following the soma pHi.

Place, publisher, year, edition, pages
Springer, 2006
Keywords
Intracellular pH, Proton channels, Fluorescence imaging, Neurones
National Category
Neurosciences
Identifiers
urn:nbn:se:liu:diva-162170 (URN)10.1007/s00424-005-0019-4 (DOI)
Available from: 2019-11-21 Created: 2019-11-21 Last updated: 2019-11-22Bibliographically approved
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