REGULATORY VOLUME DECREASE IN A RENAL DISTAL TUBULAR CELL-LINE (A6) .1. ROLE OF K+ AND CL-

Changes in volume of A6 epithelial cells were monitored by recording cell thickness (T-c). The response of T-c to a reduction of the basolateral osmolality from 260 to 140 mosmol/kg was recorded while transepithelial Na+ transport was inhibited by 20 mu M amiloride. With Cl--containing bathing media, this osmotic challenge elicited a rapid rise in T-c followed by a regulatory volume decrease (RVD). Substitution of SO42- Or gluconate for Cl- markedly reduced the RVD, whereas cells completely maintained their ability to regulate their volume after replacing Cl- by NO3-. A conductive pathway for Cl- excretion is suggested, which is insensitive to NPPB [5-nitro-2-(3-phenylpropylamino)benzoic acid], an inhibitor of some types of Cl- channels. Ba2+ (5 or 20 mM) reduced the RVD. A more pronounced inhibition of the RVD was obtained with 500 mu M quinine, a potent blocker of volume-activated K+ channels. K+-induced depolarization of the basolateral membranes of tissues incubated with SO42--containing solutions completely abolished the RVD. Noise analysis in the presence of Ba2+ showed the activation of an apical K+ conductive pathway. These results demonstrate that cell volume regulation is controlled by processes involving Cl- and K+ excretion through conductive pathways.