Na+,K(+)-
ATPase is involved in generating transmembrane ion gradients and the associated potential difference necessary for contraction of cardiac myocytes. It is possible that changes in the activity or membrane content of this
enzyme may occur under ischemic conditions. To investigate this question, right ventricular (RV)
ischemia was produced in closed chest pigs and the RV ejection fraction was measured using a fast response thermistor in the pulmonary artery. Sections of RV collected at 15, 30, 45, and 60 min of
ischemia were assayed for changes in sarcolemmal Na+,K(+)-
ATPase activity using an
enzyme coupled histochemical reaction as well as a biochemical assay. Similar sections were examined for changes in the distribution and content of Na+,K(+)-
ATPase using an immunocytochemical procedure. The RV ejection fraction fell significantly from baseline after 15 min of
ischemia (62 +/- 3% vs 39 +/- 3% respectively, P less than 0.05, n = 10). A decrease in sarcolemmal Na+,K(+)-
ATPase activity was first detected after 30 min of occlusion and a significant reduction in
enzyme activity was present at 45 min of
ischemia. In contrast no changes were detected in the distribution or content of immunoreactive Na+,K(+)-
ATPase in the sarcolemma at any time point. In addition, the amount of Na+,K(+)-
ATPase in tissue homogenates showed no significant changes after 45 min of
ischemia. These findings show that acute
ischemia results in the disruption of sarcolemmal Na+,K(+)-
ATPase activity and suggests that the decrease in
enzyme activity is not due to the loss or redistribution of sarcolemmal Na+,K(+)-
ATPase.