Sarcolemmal phospholipid fatty acid composition and permeability

In this study, the mechanism of ischaemia-induced increased sarcolemmal permeability, as manifested by release of intracellular enzymes, was investigated. The role of changes in the sarcolemmal phospholipid bilayer in this process was evaluated by experimental modulation of the phospholipid fatty acid composition. The isolated perfused rat heart subjected to low-flow hypoxia, was used as a model of global ischaemia. Glucose as well as saturated (palmitate) and unsaturated (linoleate) long-chain fatty acids were used as substrates. Hearts perfused with palmitate or linoleate (1.5 mM, fatty acid/albumin ratio, 3.4) showed a significantly higher rate of lactate dehydrogenase release in both control and ischaemic conditions than hearts perfused with glucose (10 mM). Lactate dehydrogenase release in the fatty acid-perfused hearts was associated with a significant increase in the percentage unsaturation of the sarcolemmal phospholipid fatty acids. Glucose-perfused hearts, on the other hand, showed only minor changes in the sarcolemmal phospholipid fatty acid composition. Attempts to correlate enzyme release directly with an increase in the percentage unsaturation of phospholipid fatty acids failed, since enzyme release was also stimulated in control fatty-acid-perfused hearts which (when compared with glucose) contained a higher percentage saturated phospholipid fatty acids. The results suggest that myocardial ischaemia, apart from changes in the sarcolemmal phospholipid fatty acid composition, also induces several other changes in sarcolemmal composition (e.g., cholesterol loss) which may affect is permeability for macromolecules.