Angiotensin II Stimulates Basolateral 10-pS Cl Channels in the Thick Ascending Limb

Abstract

Chloride channels in the basolateral membrane play a key role in Cl absorption in the thick ascending limb (TAL). The patch-clamp experiments were performed to test whether angiotensin II (AngII) increases Cl absorption in the TAL by stimulating the basolateral 10-pS Cl channels. AngII (1–100 nmol/L) stimulated the 10-pS Cl channel in the TAL, an effect that was blocked by losartan (angiotension AT1 receptor [AT₁R] antagonist) but not by PD123319 (angiotension AT2 receptor [AT₂R] antagonist). Inhibition of phospholipase C or protein kinase C also abolished the stimulatory effect of AngII on Cl channels. Moreover, stimulation of protein kinase C with phorbol-12-myristate-13-acetate mimicked the effect of AngII and increased Cl channel activity. However, the stimulatory effect of AngII on Cl channels was absent in the TAL pretreated with diphenyleneiodonium sulfate, an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Moreover, treatment of the TAL with diphenyleneiodonium sulfate also blocked the effect of phorbol-12-myristate-13-acetate on the 10-pS Cl channel. Western blotting demonstrated that incubation of isolated TAL with AngII increased phosphorylation of p47^phox at Ser³⁰⁴, suggesting that AngII stimulates the basolateral Cl channels by increasing NADPH oxidase–dependent superoxide generation. This notion was also supported by the observation that H₂O₂ significantly increased 10-pS Cl channel activity in the TAL. We conclude that stimulation of AT₁R increased the basolateral Cl channels by activating the protein kinase C–dependent NADPH oxidase pathway. The stimulatory effect of AngII on the basolateral Cl channel may contribute to AngII-induced increases in NaCl reabsorption in the TAL and AngII-infuse–induced hypertension.