Interaction of angiotensin II and atrial natriuretic peptide on pH(i) regulation in MDCK cells.

The effect of ANG II and atrial natriuretic peptide (ANP) on intracellular pH (pH(i)) and cytosolic free calcium concentration (Ca(2+)) was investigated in Madin-Darby canine kidney cells by using the fluorescent probes 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethyl ester (AM) and fura 2-AM or fluo 4-AM. pH(i) recovery rate was examined in the first 2 min after the acidification of pH(i) with a NH(4)Cl pulse. In the control situation, the pH(i) recovery rate was 0.088 +/- 0.014 pH units/min (n = 14); in the absence of external Na(+), this value was decreased. ANG II (10(-12) or 10(-9) M) caused an increase in this value, but ANG II (10(-7) M) decreased it. ANP (10(-6) M) or dimethyl-1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid (BAPTA)-AM (50 microM) alone did not affect this value but impaired both stimulatory and inhibitory effects of ANG II. ANG II (10(-12), 10(-9), or 10(-7) M) increased Ca(2+) progressively from 99 +/- 10 (n = 20) to 234 +/- 7 mM (n = 10). ANP or dimethyl-BAPTA-AM decreases Ca(2+), and the subsequent addition of ANG II caused a recovery of Ca(2+) but without reaching ANG II values found in the absence of these agents. The results indicate a role for Ca(2+) in regulating the process of pH(i) recovery mediated by the Na(+)/H(+) exchanger, stimulated/impaired by ANG II, and not affected by ANP or ANG II plus ANP. This hormonal interaction may represent physiologically relevant regulation in conditions of volume alterations in the intact animal.