Regulatory volume decrease in a renal distal tubular cell line (A6) I. Role of K+ and Cl−

Abstract

Changes in volume of A6 epithelial cells were monitored by recording cell thickness (T _c). The response ofT _c to a reduction of the basolateral osmolality from 260 to 140 mosmol/kg was recorded while transepithelial Na⁺ transport was inhibited by 20 μM amiloride. With Cl⁻-containing bathing media, this osmotic challenge elicited a rapid rise inT _c followed by a regulatory volume decrease (RVD). Substitution of SO₄ ²⁻ 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 μM quinine, a potent blocker of volume-activated K⁺ channels. K⁺-induced depolarization of the basolateral membranes of tissues incubated with SO₄ ²⁻-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.