Effect of ouabain on membrane conductances and volume in A6 cells

The present study reports the effect of a reduction in the Na(+)-transport rate on cell volume. A decrease in transport rate was achieved by inhibition of the basolateral Na+/K+ pump with ouabain. Cultured A6 cell monolayers were short-circuited and exposed to ouabain at the basolateral surface. In one series of experiments, cells were impaled with microelectrodes to measure cell voltage, apical fractional resistance and thus derive membrane conductances. Another set, A6, served for cell height measurements. Ouabain decreased short-circuit current (Isc), which is an index of transepithelial Na+ transport: the reduction in transport rate varied from 26 to 79% within 10 min. Equivalent circuit analysis revealed a 20% decrease in apical membrane conductance (ga), whereas basolateral membrane conductance (gb) increased by 66%. A decrease in cell voltage (12 mV) together with drop in ga during ouabain may account for the reduction in Isc. The rise in gb is mainly due to a gain in Cl- conductance which increased from 114 to 613 microS/cm2, compatible with activation of Cl- channels. All of this occurs without a detectable change in cell height. We may conclude from these data that inhibition of Na+ exit by ouabain is quickly compensated by a decrease in apical Na+ entry and an increase in basolateral Cl- conductance. Constant cell volume during ouabain implies that the total cell solute is essentially unchanged.