REPERFUSION INJURY IN CARDIAC MYOCYTES AFTER SIMULATED ISCHEMIA

The extent of cardiac injury incurred during reperfusion as opposed to that occurring during ischemia is unclear. This study tested the hypo thesis that simulated ischemia followed by simulated reperfusion cause s significant ''reperfusion injury'' in isolated chick cardiomyocytes. Cells were exposed to hypoxia, hypercarbic acidosis, hyperkalemia, an d substrate deprivation for 1 h followed by 3 h of reperfusion. Irreve rsible cell membrane injury, measured by propidium iodide uptake, incr eased from 4% of cells at the end of ischemia to 73% after reperfusion ; death occurred in only 17% of cells kept ischemic for 4 h. Lactate d ehydrogenase release was consistent with these changes. Lengthening is chemia from 30 to 90 min increased cell injury as expected, but of the total cell death, >90% occurred during reperfusion. ''Chemical hypoxi a'' composed of cyanide (2.5 mM) plus 2-deoxyglucose augmented injury before reperfusion compared with simulated ischemia. Inhibition of oxy gen radical generation by use of the metal chelator 1,10-phenanthrolin e reduced cell death from 73% to 40% after reperfusion (P = 0.001). We conclude that simulated reperfusion significantly augments the cellul ar membrane damage elicited by simulated ischemia in isolated cardiomy ocytes devoid of other factors and suggest that reactive oxygen specie s, perhaps from the mitochondria, participate in this injury.