Atrial natriuretic peptide impairs the stimulatory effect of angiotensin II on H+-ATPase.
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.
Oliveira-Souza
Maria
M
Department of Physiology and Biophysics, Instituto de Ciências Biomédicas, University of São Paulo, São Paulo, Brazil.
Malnic
Gerhard
G
Mello-Aires
Margarida
M
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004347:Drug Interactions; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
C460021:5,5'-dimethyl bis(o-aminophenoxy)ethane-N,N,N',N' tetraacetic acetoxymethyl ester; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D004533:Egtazic Acid; D009320:Atrial Natriuretic Factor; D006180:Proton-Translocating ATPases; D002118:Calcium