Cell-volume changes and ion conductances in amphibian gallbladder epithelium

Cell-volume regulation after hyposmotic swelling is common in transporting epithelial cells. Acute regulatory volume decrease is mediated in several c ell types by loss of K+ and Cl- via channels either activated by the swelli ng phenomenon or active in the cell membrane prior to swelling. In the last two decades, it has become clear that many features of cell-volume regulat ion mediated by ion fluxes vary considerably among cell types. In some inst ances, the ion channel activation, although demonstrable, is insufficient t o account, on the basis of ion fluxes, for the measured cell volume changes . Here we review the case of a salt-transporting epithelium in which hyposm otic cell swelling activates plasma membrane K+ channels, but at the same t ime inhibits Cl- channels, thus preventing an acute volume-regulatory respo nse. The sequence of events following cell swelling appears to be as follow s: K+ channels are activated by membrane stretch, the cell membrane hyperpo larizes (the voltage moves closer to the K+ equilibrium potential) and this hyperpolarization reduces the Cl- conductance, likely by a reduction in op en probability of voltage-sensitive Cl- channels. The significance of this phenomenon may be related to the preservation of intracellular Cl- rather t han cell volume, or to a physiological "need" to prevent shrinkage of cells stimulated by hormones or other mediators. Copyright (C) 2000 S. Karger AG . Basel.