DEDIFFERENTIATED CARDIOMYOCYTES FROM CHRONIC HIBERNATING MYOCARDIUM ARE ISCHEMIA-TOLERANT

Left ventricular biopsies from 21 patients with clinically diagnosed c hronic hibernating myocardium (CHM) were examined by light- and electr on microscopy. A mean of 27% of cardiomyocytes were structurally alter ed and were characterized as hibernating, because of reduced amount of myofibrils and increased glycogen content. Electron microscopy of the se cells showed reduction of T-tubules and numerous small mitochondria , but few changes associated with degeneration, acute ischemia or apop tosis. The structural changes found in CHM are reminiscent of dediffer entiation rather than degeneration. The expression patterns of some st ructural proteins show resemblance with those in embryonic cardiomyocy tes. Histochemically, mitochondrial NADH-oxidase and proton translocat ing ATPase activities were absent, whereas cytochrome c activity was p resent. Intracellular calcium distribution indicated normally bound sa rcolemmal calcium and absence of excess mitochondrial calcium accumula tion. Nuclear chromatin ranged from normal to dispersed with only a fe w nuclei that were clumped. These results suggest that cardiomyocytes from human CHM hearts are structurally altered, but viable, and lack m orphologic and cytochemical characteristics suggestive of apoptosis or acute ischemia.