Changes of Ca2+-ATPase and cytochrome oxidase activity of myocardial cell under early and late ischemia:--comparison with ultrastructural changes.

Using the histo- and cytochemical technique we assessed the Ca2+-transporting function of mitochondria (Mit) and sarcoplasmic reticulum (SR), and the ATP producing function of Mit in the ischemic myocardial cell of a dog's heart. In comparing ultrastructural ischemic changes, cytochrome oxidase (CO) and Ca2+-ATPase were cytochemically and histochemically measured when the myocardium was subjected to the ischemia of left anterior descending coronary artery occlusion for 15 min, and 60 min. After 15 min of occlusion the ischemic alterations consisted of a wide I band, decreased glycogen (G) and Mit swelling with a slight reduction of matrix density. Although CO activity was not reduced, Ca2+-ATPase had decreased mainly in Mit. Sixty min of ischemia resulted in loss of G, intermyofibrillar edema, marked Mit swelling with loss of matrix density and partial disruption of cristae, and dilatation of SR. Ca2+-ATPase activity was significantly reduced in Mit, SR and myofibrils. Although there was Mit swelling with partial disruption of cristae after 60 min of ischemia, CO activity was found to still exist in the remaining cristae. These findings suggest that intracellular organelle dysfunction progresses in the ischemic myocardial cell at different rates, and that disruption of intracellular Ca2+-homeostasis may occur early in the ischemic state.