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

Abstract

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.