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 c ell thickness (T-c). The response of T-c to a reduction of the basolat eral osmolality from 260 to 140 mosmol/kg was recorded while transepit helial Na+ transport was inhibited by 20 mu M amiloride. With Cl--cont aining bathing media, this osmotic challenge elicited a rapid rise in T-c followed by a regulatory volume decrease (RVD). Substitution of SO 42- Or gluconate for Cl- markedly reduced the RVD, whereas cells compl etely maintained their ability to regulate their volume after replacin g Cl- by NO3-. A conductive pathway for Cl- excretion is suggested, wh ich is insensitive to NPPB [5-nitro-2-(3-phenylpropylamino)benzoic aci d], an inhibitor of some types of Cl- channels. Ba2+ (5 or 20 mM) redu ced 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 incub ated with SO42--containing solutions completely abolished the RVD. Noi se analysis in the presence of Ba2+ showed the activation of an apical K+ conductive pathway. These results demonstrate that cell volume reg ulation is controlled by processes involving Cl- and K+ excretion thro ugh conductive pathways.