Relationship between energy liberation and utilization in ischemic cardiac muscle

Mitochondrial respiration, succinate dehydrogenase coenzyme Q reductase, and myosin B were investigated in ischemic myocardium from experimental myocardial infarction in dogs. Respiratory control ratio of mitochondria was impaired by ischemia at 60 min after coronary ligation, and oxygen consumption was inhibited 120 min later. Enzyme activity of succinate dehydrogenase coenzyme Q reductase was decreased at 6 hr after coronary ligation. Calcium ion sensitivity of myosin B declined 12 hr after coronary ligation. However, adenosine triphosphatase activity of myosin A from infarcted myocardium was not different from that of the intact one. These results suggest that interaction in the sequence of enzyme complexes was first impaired in ischemic myocardium and that deterioration of enzyme activity was then manifested.