Sarcolemmal enzymes and Na+ -Ca2+ exchange in hypoxic, ischemic, and reperfused rat hearts.

Isolated spontaneously beating rat hearts were perfused in the Langendorff mode and divided into four groups, i.e., control (aerobic), hypoxic (95% N2-5% CO2), ischemic, and ischemic reperfused. After a total of 90 min of perfusion, the sarcolemma was isolated and enzymatically characterized. Ouabain-sensitive Na+-K+-ATPase was inhibited in all three experimental groups, whereas K+-stimulated phosphatase activity was decreased only in the ischemic and reperfused groups compared with control. 5'-Nucleotidase activity was inhibited (P less than 0.05) only in the ischemic group. Mg2+-ATPase activity was not different from control. Passive Ca2+ uptake and Ca2+ efflux were not significantly altered by any of the interventions. Na+-Ca2+ exchange rate, but not capacity, was decreased (by 32-42%) in the ischemic group but this was partially reversed on reperfusion. These results suggest that changes secondary to lack of flow rather than O2 play a major role in the etiology of ischemic damage to the membrane and that a 15-min period of reperfusion after 60 min of ischemia does not exacerbate this damage.