SARCOLEMMAL CALCIUM-TRANSPORT IN CONGESTIVE-HEART-FAILURE DUE TO MYOCARDIAL-INFARCTION IN RATS

Because Na+-Ca2+ exchange and Ca2+ pump are thought to play a role in sarcolemmal Ca2+ movements, we examined the Na+-dependent Ca2+-uptake and ATP-dependent Ca2+-uptake activities in failing heart after myocardial infarction in rats. The left coronary artery was ligated, and the viable left ventricle was used 4, 8, and 16 wk later; sham-operated animals served as controls. Increased left ventricular diastolic pressure and decreased positive and negative change in pressure over time were observed in experimental animals at 4, 8, and 16 wk; these changes were associated with accumulation of fluid in the abdominal cavity. The sarcolemmal Na+-dependent Ca2+ uptake was depressed in 4-, 8-, and 16-wk experimental hearts. The decrease in sarcolemmal Na+-dependent Ca2+ uptake in failing hearts was seen when the activity was assayed either as a function of time or Ca2+ concentration; a depression of maximal velocity without any change in activity constant for Ca2+ was observed. No alteration in the Ca2+ pump (ATP-dependent Ca2+ accumulation and Ca2+-stimulated adenosinetriphosphatase) activities was evident in the 4-, 8-, and 16-wk experimental groups. These data suggest that changes in the Na+-dependent Ca2+ handling by the sarcolemmal membrane may be associated with contractile abnormalities in this model of congestive heart failure.