Endothelin and Angiotensin II Stimulation of Na

We compared the effects of endothelin-1 (ET-1) on intracellular pH, intracellular [Ca 2 1 ] i , and cell contraction in hypertrophied adult ventricular myocytes from ascending aortic banded rats and age-matched controls. Intracellular pH (pH i ) was measured in individual myocytes with SNARF-1, and [Ca 2 1 ] i was measured with indo-1, simultaneous with cell motion. Experiments were performed at 36 8 C in myocytes paced at 0.5 Hz in Hepes-buffered solution (pH o 7.40) containing 1.2 mM CaCl 2 . At baseline, calibrated pH i , diastolic and systolic [Ca 2 1 ] i values, and the amplitude of cell contraction were similar in hypertrophied and control myocytes. Exposure of the control myocytes to 10 nM ET-1 caused an increase in the amplitude of cell contraction to 163 6 22% of baseline ( P , 0.05), associated with intracellular alkalinization (pH i 1 0.08 6 0.02 U, P , 0.05) and a slight increase in peak systolic [Ca 2 1 ] i (104 6 1% of baseline, P , 0.05). In contrast, in the hypertrophied myocytes, exposure to ET-1 did not increase the amplitude of cell contraction or cause intracellular alkalinization ( 2 0.01 6 0.02 U, NS). Similar effects were observed in the hypertrophied and control myocytes in response to exposure to 10 nM angiotensin II. ET-1 also increased the rate of recovery from intracellular acidosis induced by the washout of NH 4 Cl in the control cells, but did not do so in the hypertrophied cells. In the presence of 10 m M 5-( N -ethylN -isopropyl)-amiloride, which inhibits Na 1 -H 1 exchange, ET-1 did not cause a positive inotropic effect or intracellular alkalinization in control cells. The activation of protein kinase C by exposure to phorbol ester caused intracellular alkalinization and it increased the rate of recovery from intracellular acidification induced by an NH 4 Cl pulse in control cells but not in hypertrophied cells. ET-1, as well as angiotensin II, and phorbol ester, fail to stimulate forward Na 1 -H 1 exchange in adult hypertrophied myocytes. These data suggest a defect in the coupling of protein kinase C signaling with Na 1 -H 1 exchange in adult hypertrophied myocytes. ( J. Clin. Invest. 1997. 99: 125–135.)