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  • 1.
    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 laevis1998In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 165, no 2, p. 175-181Article in journal (Refereed)
    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.

  • 2.
    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 density1998In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 165, no 2, p. 183-189Article in journal (Refereed)
    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.

  • 3.
    Sjö, Anita
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology .
    Magnusson, Karl-Eric
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology .
    Holmgren Peterson, Kajsa
    Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
    Association of a-dystrobrevin with reorganizing tight junctions2005In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 203, no 1, p. 21-30Article in journal (Refereed)
    Abstract [en]

    Alpha-dystrobrevin (a-DB) has been described primarily as a cytoplasmic component of the dystrophin-glycoprotein complex in skeletal muscle cells. Isoforms of a-DB show different localization in cells and tissues, at basolateral membranes in epithelial cells, dystrobrevins mediate contact with the extracellular matrix, peripheral and transmembrane proteins and the filamentous actin cytoskeleton. Beside their structural role, a-DBs are assumed to be important in cell signalling and cell differentiation. We have primarily assessed the role of a-DB in two epithelial cell lines (MDCK I, HT 29), which represent different developmental stages and exhibit distinct permeability characteristics. Using a polyclonal anti-a-DB antibody, we have investigated its expression, localization and association with tight junction (TJ)- associated proteins (ZO-1, occludin) before and after protein kinase C (PKC) activation with phorbol myristate acetate. Distinct subsets of a-DB isoforms were detected in the two cell lines by immunoblotting. In both cell lines there was submembranous localization of a-DB both apically and basolaterally, shown with confocal imaging. PKC activation caused a reorganization of TJ, which was parallel to increased localization of a-DB to TJ areas, most pronounced in MDCK I cells. Moreover, actin and ZO-1 co-immunoprecipitated with a-DB, as displayed with immunoblotting. Our findings suggest that a-dystrobrevin specifically is associated with the tight junctions during their reorganization. © Springer Science+Business Media, Inc. 2005.

  • 4.
    Sjö, Anita
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
    Magnusson, Karl-Eric
    Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
    Holmgren Peterson, Kajsa
    Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
    Protein kinase C activation has distinct effects on the localization, phosphorylation and detergent solubility of the claudin protein family in tight and leaky epithelial cells2010In: Journal of Membrane Biology, ISSN 0022-2631, E-ISSN 1432-1424, Vol. 236, no 2, p. 181-189Article in journal (Refereed)
    Abstract [en]

    We have previously shown that protein kinase C (PKC) activation has distinct effects on the structure and barrier properties of cultured epithelial cells (HT29 and MDCK I). Since the claudin family of tight junction (TJ)-associated proteins is considered to be crucial for the function of mature TJ, we assessed their expression patterns and cellular destination, detergent solubility and phosphorylation upon PKC stimulation for 2 or 18 h with phorbol myristate acetate (PMA). In HT29 cells, claudins 1, 3, 4 and 5 and possibly claudin 2 were redistributed to apical cell-cell contacts after PKC activation and the amounts of claudins 1, 3 and 5, but not of claudin 2, were increased in cell lysates. By contrast, in MDCK I cells, PMA treatment resulted in redistribution of claudins 1, 3, 4 and 5 from the TJ and in reorganization of the proteins into more insoluble complexes. Claudins 1 and 4 were phosphorylated in both MDCK I and HT29 cells, but PKC-induced changes in claudin phosphorylation state were detected only in MDCK I cells. A major difference between HT29 and MDCK I cells, which have low and high basal transepithelial electrical resistance, respectively, was the absence of claudin 2 in the latter. Our findings show that PKC activation targets in characteristic ways the expression patterns, destination, detergent solubility and phosphorylation state of claudins in epithelial cells with different capacities to form an epithelial barrier.

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