Basolateral membrane conductance in A6 cells: effect of high sodium transport rate

Conductance of apical and basolateral membranes in short-circuited cultured renal distal cells (A6) was determined using microelectrodes. Epithelia were pre-incubated with 0.1 mumol/l dexamethasone in the presence of 4 mumol/l amiloride to prevent increase in apical Na+ entry. Omission of amiloride increased the Isc from 5.7 to 27.6 microA/cm2 due to the rise in apical membrane conductance from 21 to 595 microS/cm2. Apical fractional resistance decreased from 0.89 to 0.40 and cells depolarized from -52 to -4 mV. Basolateral membrane conductance, which was 320 microS/cm2 at partially inhibited transport, was not significantly altered during the first 2 min following establishment of high transport activity; it started to increase thereafter reaching a more than threefold higher value of 1324 microS/cm2 within 12 min. The gain cannot be explained by increase in partial K+ conductance. Disappearance of the conductance after reduction of basolateral Cl- or in the presence of the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate indicates a Cl- conductance, which appears to be activated by depolarization.