Volume regulatory Cl- loss after Na+ pump inhibition in CCT principal cells

Ouabain caused rabbit cortical collecting tubule (CCT) principal cells to swell 53% and then undergo regulatory volume decrease (RVD) at a rate of 4%/min to a new steady-state volume 10% below control. Reduction of peritubular Cl- concentration transiently depolarized transepithelial potential (Vte) by 36 mV and stimulated the rate of RVD 30-fold. Peritubular application of 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) inhibited RVD 74%. In contrast, luminal Cl- reduction or application of DIDS had no effect on RVD. A 10-fold elevation of perfusate K+ caused volume-regulated cells to swell 23% at a rate of 60%/min. Removal of luminal Cl- had no effect on either the rate or magnitude of K+ swelling. Peritubular or bilateral Cl- removal, however, inhibited the rate of K+ swelling by 96 and 99%, respectively. Substitution of bath Cl- for Br-, SCN-, or I- inhibited the rate of K+ swelling by 40, 38, and 98%, respectively. Surprisingly, NO3- inhibited the rate of K+ swelling by 82%. All Cl- substitutes tested transiently depolarized Vte by 3-49 mV. These results suggest strongly that RVD is mediated by a basolateral Cl- channel with a high selectivity for Cl- over other anions.