EFFECT OF LOW CALCIUM ON HIGH-ENERGY PHOSPHATES AND SARCOLEMMAL NA+/K+-ATPASE IN THE INFARCTED-REPERFUSED HEART

This study was undertaken to compare the effect of low to normal serum calcium on biochemical parameters in the myocardium of dogs subjected to 90 min of coronary artery ligation followed by 30 min reperfusion. The accumulation of calcium, the decrease of adenosine triphosphate (ATP) and creatine phosphate (CP) and the inhibition of sarcolemmal ouabain-sensitive Na+/K+-ATPase which are prominent findings in the ischemic-reperfused myocardium, were studied under normal and low serum Ca produced by normal and modified hemodialysis (HD). The results showed a lower accumulation of Ca (P < 0.002) in the ligated-reperfused myocardium of dogs subjected to low-calcium HD. In the same group of animals ATP was protected to some extent while CP was completely preserved. This may indicate that during reperfusion with low Ca, restored ATP is further utilized for CP regeneration. The activity of Na+/K+-ATPase was within normal values in the ligated-reperfused myocardium of the low-calcium group. The significantly (P < 0.001) negative correlation between tissue calcium concentration and Na+/K+-ATPase activity under various conditions examined, provided additional evidence that low calcium is a protective factor of the enzyme activity during ischemia and reperfusion.