We propose to study the mechanisms by which myocardial membranes and organelles are injured during ischemia. We will focus our attention on enzymes that hydrolyze lipids (phospholipids, triacylglycerols, fatty acyl CoA, etc.). During ischemia, lipases may become activated by various mechanisms. In addition, normally sequestered lipases may be released, thus gaining access to substrates. Activation and/or redistribution of lipases during ischemia may be due to acidosis, increased concentrations of CA++, loss of ATP, dephosphorylation, accumulation of lipid metabolites, etc. Moreover, the susceptibility of myocardial lipids to hydrolysis by lipases may also be altered by these factors during ischemia. Membrane bound enzyme activities, integrity of sarcolemma, lysosomes and sarcoplasmic reticulum may be altered during ischemia by lipolysis and accumulated lipid metabolites. In the proposed studies, evidence will be sought for activation or redistribution of lipases, changes in membrane lipid composition, and changes in functional properties of membrane bound enzymes and organelles during ischemia. The lipids of specific organelles (sarcolemma, sarcoplasmic reticulum, lysosomes, etc.) obtained from ischemic tissue will be analyzed to determine which are most susceptible to hydrolysis, both during ischemia, and by endogenous and exogenous lipases during subsequent in vitro incubations. During these in vitro incubations, particular attention will be paid to free fatty acids, lysophospholipids, acyl CoA, prostaglandins and metabolites such as ATP to determine their ability to alter membrane susceptibility to lipolysis as well as to perturb membrane and organelle function. Effects of pharmacological agents on ischemia-induced changes in lipase activities, membrane lipid composition and membrane function will be examined. The overall purpose of this work will be to understand the injury process during ischemia at the cellular and molecular level. Such knowledge may enable better therapeutic approaches to myocardial injury in man.