Sarcolemmal Ca2+ transport in streptozotocin-induced diabetic cardiomyopathy in rats.

Heart sarcolemmal membranes were isolated by the sucrose density gradient method from rats with chronic diabetes induced by a streptozotocin (65 mg/kg iv) injection. Na+-dependent Ca2+-uptake activities were significantly depressed in diabetic sarcolemmal membranes; such alterations were evident at different incubation times and at different concentrations of Ca2+. Administration of insulin to diabetic rats normalized the Na+-dependent Ca2+-uptake activities. ATP-dependent Ca2+ accumulation and Ca2+-stimulated Mg2+-dependent ATPase, which represents Ca2+-pump mechanisms, were significantly depressed in sarcolemmal preparations for diabetic rats and these changes were also reversible upon insulin treatment. An increase in lysophosphatidylcholine and a decrease in phosphatidylethanolamine as well as diphosphatidylglycerol contents were observed in heart membranes isolated from diabetic rats but other phospholipids were unchanged. Cholesterol-to-phospholipid ratio was significantly increased in preparations from diabetic rats. These results indicate a depression in the ability of the cell to remove Ca2+ through Na+-Ca2+ exchange and Ca2+-pump mechanisms in sarcolemma, and these defects may contribute to the occurrence of intracellular Ca2+ overload and diabetic cardiomyopathy.