Background: The effects of arginine vasopressin (AVP) on intracellular pH (pHi) are not clearly defined, and may vary with cell membrane surface and the hormonal doses being studied. Since cytosolic free calcium concentration ([Ca2+]i) has an important effect on cellular H+ extrusion and it was shown that AVP increases [Ca2+]i while atrial natriuretic peptide (ANP) reduces it, there may be some interaction between AVP and ANP during the regulation of pHi.
Methods: The effects of AVP and/or ANP on pHi and [Ca2+]i were investigated in Madin-Darby canine kidney (MDCK) cells by the fluorescent probes BCECF-AM and Fluo 4-AM, respectively. The pHi recovery rate was examined in the first two minutes following the acidification of pHi with a NH4Cl pulse.
Results: AVP (10(-12) or 10(-9) mol/L) stimulated the rate of the Na+-dependent pHi recovery, but AVP (10(-6) mol/L) impaired it. At the apical membrane surface, specific V1 or V2 receptor antagonists did not alter the effects of AVP. At the basolateral membrane surface, the V1 antagonist returned both the stimulatory and inhibitory effects of AVP to control levels, and the V2 antagonist converted the inhibitory effect of AVP to a stimulatory effect. ANP (10(-6) mol/L) or dimethyl-BAPTA-AM (50 micromol/L) impaired both the stimulatory and inhibitory effects of AVP. AVP increased [Ca2+]i in a dose-dependent manner. ANP or dimethyl-BAPTA-AM decreased [Ca2+]i, and the subsequent addition of AVP caused only a partial recovery of [Ca2+]i.
Conclusions: The results are compatible with stimulation of the Na+/H+ exchanger by increases of [Ca2+]i in the lower range (at 10(-12) or 10(-9) mol/L AVP, via basolateral V1 receptors) and inhibition at high [Ca2+]i levels (at 10(-6) mol/L AVP, via basolateral V1 and V2 receptors). ANP, by impairing the path causing the increase in [Ca2+]i, blocks both the stimulatory and inhibitory effects of AVP on Na+-dependent pHi recovery.
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