Angiotensin II stimulates vesicular H+-ATPase in rat proximal tubular cells

AUTOR(ES)

Wagner, Carsten A.

FONTE

The National Academy of Sciences

RESUMO

Two mechanisms of H+ ion secretion in the proximal tubule that mediate bicarbonate reabsorption have been identified: the brush border Na/H exchanger and electrogenic H+ ion secretion. Angiotensin II (AII) has been shown to be a regulator of the luminal Na+/H+ exchanger and the basolateral Na+/HCO3− cotransporter. In the present study, we examined the effects of AII on H+-ATPase activity in isolated proximal tubule fragments. H+-ATPase activity was assessed by monitoring intracellular pH after Na+ removal from the bath. In addition, we investigated the effects on pH recovery of the proton pump inhibitor bafilomycin A1, removal of Cl−, and of colchicine. pH was continuously measured with the pH-sensitive fluorescent dye 2′, 7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Recovery of cell pH was observed in the absence of external Na+ and was significantly accelerated by AII. The AII-stimulated pH recovery was completely abolished by bafilomycin A1, by removal of Cl−, by NPPB [5-nitro-2-(3-phenylpropylamino)-benzoate; a potent Cl− channel blocker], and by colchicine. We conclude from these studies that AII stimulates proton extrusion via H+-ATPase by a Cl−-dependent process involving brush border insertion of vesicles. This process may contribute to up-regulation of HCO3− reabsorption along the proximal tubule when tubules are exposed to AII.

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