Roles of external and cellular Cl- ions on the activation of an apical electrodiffusional Cl- pathway in toad skin.
This study is concerned with the short-circuit current, Isc, responses of the Cl(-)-transporting cells of toad skin submitted to sudden changes of the external Cl- concentration, [Cl]o. Sudden changes of [Cl]o, carried out under apical membrane depolarization, allowed comparison of the roles of [Cl]o and [Cl]cell on the activation of the apical Cl- pathways. Equilibration of short-circuited skins symmetrically in K-Ringer's solutions of different Cl- concentrations permitted adjustment of [Cl]cell to different levels. For a given Cl- concentration (in the range of 11.7 to 117 mM) on both sides of a depolarized apical membrane, this structure exhibits a high Cl- permeability, P(Cl)apical. On the other hand, for the same range of [Cl]cell but with [Cl]o = 0, P(Cl)apical is reduced to negligible values. These observations indicate that when the apical membrane is depolarized P(Cl)apical is modulated by [Cl]o; in the absence of external Cl- ions, intracellular Cl- is not sufficient to activate P(Cl)apical. Computer simulation shows that the fast Cl- currents induced across the apical membrane by sudden shifts of [Cl]o from a control equilibrium value strictly follow the laws of electrodiffusion. For each experimental group, the computer-generated Isc versus [( Cl]cell - [Cl]o) curve which best fits the experimental data can only be obtained by a unique pair of P(Cl)apical and Rb (resistance of the basolateral membrane), thus allowing the calculation of these parameters. The electrodiffusional behavior of the net Cl- flux across the apical membrane supports the channel nature of the apical Cl- pathways in the Cl(-)-transporting cells. Cl- ions contribute significantly to the overall conductance of the basolateral membrane even in the presence of a high K concentration in the internal solution.
Departamento de Fisiologia e Biofísica, Universidade de São Paulo, Brazil.
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Procopio
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Lacaz-Vieira
D000818:Animals; D001693:Biological Transport, Active; D002024:Bufo marinus; D002463:Cell Membrane Permeability; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D003198:Computer Simulation; D004058:Diffusion; D004553:Electric Conductivity; D007473:Ion Channels / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D012867:Skin / Q000378:metabolism*; D012879:Skin Physiological Phenomena
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins