In tissue, mechanical cell-to-cell interactions may contribute to cardiomyocyte injury in anoxia-reoxygenation. In the present study, the disturbance of energy metabolism and cell injury were investigated in isolated cardiomyocytes, free of external mechanical constraints. Cardiomyocytes from adult rat, attached to culture dishes, were exposed to 120 min of anoxia and 15 min of reoxygenation in a substrate-free modified Tyrode solution. The energetic state of the cells in anoxia-reoxygenation was characterized by the free-energy change of ATP hydrolysis (delta GATP), amounting to 57 kJ/mol ATP in normoxia. After 120 min of anoxia, all cells were contracted to 65% of their length and delta GATP decreased to 41 kJ/mol. No lactate dehydrogenase was released. Reoxygenation caused a partial oxygen paradox: immediate hypercontracture of the cells, but no release of lactate dehydrogenase. delta GATP recovered to 51 kJ/mol within 15 min. The results demonstrate that anoxic cardiomyocytes can be energy depleted without losing sarcolemmal integrity. They can undergo hypercontracture, elicited by reoxygenation, and yet an almost normal delta GATP can be reestablished.
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