Loss of functional and structural integrity of the sarcolemma: an early indicator of irreversible injury of myocardium?

The purpose of this study was to explore the relationship between the extent of sarcolemmal damage observed 2 h after reperfusion of myocardium which had been ischemic for either 0.5 or 1 h and the long-term recovery of function of that same myocardium. For this purpose we studied the Ca2+ pumping ATPase activity and protein phosphorylation of sarcolemmal vesicles isolated after 2 h reperfusion. Both activities declined depending on the duration of ischemia, which suggests the development of sarcolemmal Ca2+ pump failure. Morphological examination of the sarcolemma by thin-section and freeze-fracture electronmicroscopy, in biopsies obtained after 2 h of reperfusion, showed severe clustering of intramembranous particles and formation and extrusion of lipidic liposomal structures which also depended on the duration of ischemia. Except for the occurrence of minor particle aggregation in the samples which had been ischemic for 0.5 h, sarcolemmal disruption was only seen in those myocardial segments which had been subjected to 1 h of coronary artery ligation. Recovery of regional myocardial function, assessed by 2-D-echocardiography after 2 weeks of reperfusion, was closely related to the degree to which sarcolemmal integrity was maintained after 2 h reperfusion.