Regulation of lipolysis in myocardial cells from diabetic rat hearts

Abstract

REGULATION OF LIPOLYSIS IN MYOCARDIAL CELLS FROM DIABETIC RAT HEARTS. D.L. Severson, K. Kenno, T. Larsen, I. Pmmirez. Department of Pharmacology and Therapeutics, University of Calgary, Calgary, Canada. The acute induction of diabetes (I00 mg/kg streptozotocin; 3-4 days) resulted in an elevation in the triacylglycerol (TG) content of calcium-tolerant myocardial cells, and increased rates of lipolysis (glycerol output) during subsequent incubations. The release of glycerol into the medium was accompanied by a stoiehiometric decline in TG content. Isoproterenol and cyclic AMP analogs did not produce the same foldstimulation of glycerol output from diabetic myocytes as with control myocytes. Similar results were obtained with myocytes from a chronic model of diabetes (70 mg/kg; 28 days). Myocardial cells contain three distinct TG lipase activities: an acid lysosomal lipase, lipoprotein lipase (LPL), and a unique neutral lipase (NL). Diabetes resulted in a decrease in LPL activity in myocyte homogenates and in particulate subcellular fractions, but the percentage of cellular LPL activity released into the medium after incubation of the myocytes with heparin was normal. In contrast, NL activity was increased in diabetic myocyte homogenates and microsomal fractions. Acid lipase activity was not changed by diabetes.