Lipids of myocardial membranes: susceptibility of a fraction enriched in sarcolemma to hydrolysis by an exogenous mammalian phospholipase A2.

A myocardial membrane fraction enriched in sarcolemma was used to determine the susceptibility of the lipids to hydrolysis by a phospholipase A2 from granulocytes. After incubation (37 C, pH 7.0, 5 mM Ca2+) with the phospholipase A2 for 30 min, a more than 3-fold increase in unesterified fatty acids was found (up to 47 nmol/mg protein; P < 0.001) relative to a control incubated without phospholipase A2 or Ca2+. This included a 10-fold increase in the arachidonic acid content (up to 42 mol%) and at least a 7-fold increase in lysophosphatidylethanolamine (up to 7.4 mol% total phospholipid-P). However, the exogenous phospholipase did not augment the quantity of lysophosphatidylcholine produced by endogenous phospholipases in the presence of Ca2+ (5 mM). These results demonstrate the in vitro susceptibility of phospholipids of myocardial membranes, particularly phosphatidylethanolamine, to the neutral-active, Ca2+-dependent phospholipase A2 from granulocytes. This work may be relevant to myocardial inflammation and tissue damage during ischemia, where heterolytic injury of the myocardium may occur subsequent to the accumulation of granulocytes.