Objective: The aim was to characterise the effects of angiotensin II on Na+/H+ exchange in adult ventricular myocytes.
Methods: Intracellular pH (pHi) was continuously measured with the fluorescent pH indicator, SNARF-1, in single resting myocytes obtained from adult rabbits by enzymatic dissociation. In some experiments cells were electrically paced to elicit contractions. All experiments were performed at 36 degrees C in HEPES buffered solution containing no added CO2 or HCO3- (pHo 7.4).
Results: Rapid application of angiotensin II caused pHi to rise. The initial rate of rise and initial net H+ efflux responded to angiotensin II in a concentration dependent manner, EC50 = 7.8. Buffering of cytosolic calcium with the calcium chelator BAPTA did not affect the initial net H+ efflux elicited by 1 microM angiotensin II. The increase in steady state pHi was blocked by inhibitors of Na+/H+ exchange, amiloride (1 mM) and EIPA (10 microM). Angiotensin II also increased the rate of pHi recovery from intracellular acidosis at pHi values above approximately 6.9. During inhibition of Na+/H+ exchange the application of angiotensin II decreased steady state pHi. This acidosis was blocked by preincubation in dextrose-free solution containing 20.0 mM 2-deoxy-D-glucose and 10 microM EIPA. The positive inotropic effect of angiotensin II was markedly suppressed by amiloride.
Conclusions: Angiotensin II exerts a concentration dependent stimulatory effect on Na+/H+ exchange in adult rabbit ventricular myocytes. This effect does not appear to involve changes in cytosolic calcium. During inhibition of Na+/H+ exchange, angiotensin II causes pHi to fall, perhaps by stimulating metabolic acid production. The positive inotropic action of angiotensin II depends, in part, on stimulation of Na+/H+ exchange.