Effect of ANG II on pHi, [Ca2+]i, and contraction in rabbit ventricular myocytes from infarcted hearts

Abstract

In this study we examined Na+/H+exchange activity, Ca2+transients, and contractility in rabbit ventricular myocytes isolated from normal and chronically (8–12 wk) infarcted left ventricles. Myocytes from infarcted hearts (post-MI myocytes) were isolated from the peri-infarcted region of the left ventricle. Intracellular pH (pHi) and Ca2+ concentration ([Ca2+]i) were measured with the fluorescent pH indicators seminaphthorhodafluor 1 and fluo 3, respectively, and contractility was assessed from changes in cell shortening during field stimulation. Experiments were performed at extracellular pH 7.4 in the presence and absence (HEPES buffer) of CO2 and[Formula: see text]. Our findings demonstrate that 1) myocytes after myocardial infarction (post-MI) were significantly larger than normal, 2) post-MI hypertrophy was not accompanied by changes in non-CO2intracellular buffering power, 3) post-MI hypertrophy did not significantly affect the ability of Na+/H+exchange to mediate pHi recovery from intracellular acidosis, 4) the stimulatory effect of ANG II (100 nM) on Na+/H+exchange was significantly reduced in post-MI myocytes, 5) in[Formula: see text]-buffered solutions, ANG II did not significantly stimulate pHirecovery from acidosis in post-MI myocytes, 6) the angiotensin AT1 receptor mediates the stimulatory action of ANG II on Na+/H+exchange in normal and post-MI myocytes, and 7) the stimulatory effect of ANG II on the Ca2+ transient and contraction was blunted in post-MI myocytes bathed in HEPES-buffered solution. A suppressed ventricular responsiveness to ANG II may be beneficial in the intact myocardium by attenuating ATP consumption and by reducing intracellular Na+accumulation during ischemia-reperfusion.