AMELIORATION OF ISCHEMIC CALCIUM OVERLOAD CORRELATES WITH HIGH-ENERGYPHOSPHATES IN SENESCENT MYOCARDIUM

Previously, we have shown that potassium and magnesium (K-Mg, 20 mM ea ch) cardioplegia ameliorated cytosolic calcium ([Ca2+](i)) accumulatio n and was associated with enhanced functional recovery after surgicall y induced global ischemia in the aged heart. K-Mg cardioplegia was als o shown to enhance cytosolic cytochrome oxidase I activity and mRNA le vels, suggesting that enhanced functional recovery may involve the pre servation of high-energy phosphates. To investigate this hypothesis, P -31 nuclear magnetic resonance was used to measure serial alterations in phosphocreatine (PCr), inorganic phosphate, nucleoside triphosphate (NTP), intracellular free magnesium (Mg-f), and intracellular pH (pH( i)) in Langendorff-perfused, aged (135 Nk) rabbit hearts during preisc hemia, global ischemia (30 min), and reperfusion (30 min). K-MET cardi oplegia retarded PCr depletion (P < 0.05) and significantly enhanced N TP preservation (P < 0.05) during ischemia and reperfusion. K-Mg cardi oplegia also attenuated the increase in Mg-f during ischemia (P < 0.05 ). These results were correlated with amelioration of [Ca2+](i) accumu lation during ischemia and preservation of left ventricular function a fter reperfusion and suggest that optimal functional recovery from sur gically induced ischemia is provided by K-Mg cardioplegia in the aged myocardium.