Impaired sarcolemmal membrane permeability in reperfused ischemic myocardium. Ultrastructural tracer study.

Sarcolemmal membrane permeability to intravenously injected horseradish peroxidase HRP (MW = 40,000) was examined in 8 Wistar rats which had temporary ischaemia produced by left coronary artery ligation. HRP reaction product was identified following 6 min of circulation time by light and electron microscopy. Controls included 4 uninjected animals with coronary ligation, 2 uninjected animals without myocardial ischaemia and 2 injected non operated rats. In normal myocardium, the tracer permeated endothelial plasmalemmal vesicles, intercellular spaces and intracellular vesicle of the T-tubule system, but never permeated the cytoplasm of myocardium cells. As early as 15 min after coronary artery ligation followed by 6 min of reperfusion with circulation of the tracer, HRP product could be seen in the cytoplasm of muscle cells randomly distributed in the subendocardial area. The quantity of permeated cells increased when the ischaemic myocardium is reperfused during 10 min before injecting the tracer. These data indicate that sarcolemmal membrane alteration is an early event in myocardial ischaemic injury and precede the irreversible cellular degenerative changes.