Selectivity of maxi chloride channels in the L6 rat muscle cell line.
A method is described for the determination of reversal potentials (EREV) from variance of single-channel currents vs. membrane potential in ramp pulse mode. The variance-voltage relationship is represented by a parabola with a minimum of the best fit curve corresponding to the value of EREV. The reversal potential of the maxi-Cl channels changes according to the activity of Cl ions at the internal side of the excised (inside-out) patch membrane as expressed by the Goldman-Hodgkin-Katz equation with PA/PCl = 0.15, indicating the anion nature of the channel. The relative permeabilities (PA/PCl found for halide anions, were 1.15 for iodide and 1.18 for bromide. The relative permeabilities measured (PA/PCl) for other anions were 1.13 for nitrate, 0.59 for bicarbonate, 0.60 for methanesulfonate, 0.40 for SO42-, 0.44 for propionate, and 0.10 for glutamate. No significant differences in PA/PCl of the investigated anions were observed between proliferating myoballs and quiescent myoblasts. This may mean that the newly formed channels possess full-grown selective filters. A close correlation (r = 0.89) was found between the calculated Stokes diameters of the anions under investigation and their relative permeabilities (PA/PCl). The intercept of the best fit line with the abscissa is 7.2 A (7.2 x 10(-10)m), which may correspond to the diameter of the selectivity filter of the maxi-chloride channel in L6 myoblasts. A similar value of the channel size was obtained from the relationship between the minimum cross-sectional areas of the anions and their relative permeabilities, PA/PCl. The best fit line intercepts the abscissa at 27.5 A2, indicating a pore size approximately 6 A. The minimum areas were obtained by computer from molecular models of the anions.
Hurnák
O
O
Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovakia.
Zachar
J
J
D000818:Animals; D000838:Anions / Q000737:chemistry / Q000378:metabolism; D001965:Bromides / Q000378:metabolism; D002460:Cell Line; D002463:Cell Membrane Permeability; D018118:Chloride Channels / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D004594:Electrophysiology / Q000379:methods; D007454:Iodides / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D008958:Models, Molecular; D009132:Muscles; D051381:Rats
D000838:Anions; D001965:Bromides; D018118:Chloride Channels; D002712:Chlorides; D007454:Iodides