Background: Angiotensin II (Ang II) action on H+-ATPase is not clearly defined, and may vary with renal tubule segment and hormonal doses being studied. Since an increase of cytosolic calcium ([Ca2+]i) can stimulate acid vesicle movement and exocytotic insertion of proton pumps, and it has been shown that Ang II increases [Ca2+]i while atrial natriuretic peptide (ANP) reduces it, there may be some interaction between Ang II and ANP in the regulation of intracellular pH (pHi) mediated by H+-ATPase.
Methods: The effects of Ang II and/or ANP on the regulation of pHi via H+-ATPase and of [Ca2+]i was investigated in Madin-Darby canine kidney cells (MDCK) by the fluorescent probes BCECF-AM and Fluo-4/AM, respectively. The pHi recovery rate was examined following the intracellular acidification after an NH4Cl pulse, in presence of zero Na+ plus Schering 28080, which is a specific inhibitor of H+/K+-ATPase.
Results: Ang II (10-12, 10-9 or 10-7 mol/L) increased the rate of pHi recovery and [Ca2+]i in a dose-dependent manner. ANP (10-6 mol/L) or dimethyl-BAPTA/AM (5 x 10-5 mol/L, an intracellular calcium chelator) did not affect the pHi recovery but decreased [Ca2+]i and blocked the stimulatory effect of Ang II on the pHi recovery.
Conclusions: The results suggest that the increase of [Ca2+]i regulates the dose-dependent stimulatory effect of Ang II on H+-ATPase. ANP or dimethyl-BAPTA/AM, by impairing the path causing the increase in [Ca2+]i, blocks this stimulatory effect of Ang II.
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