Ischemia-induced alteration of myocardial Na+-K+-ATPase activity and ouabain binding sites in hypercholesterolemic rabbits

The purpose of this study was to explore the effect of ischemia on the Na+-K+-ATPase activity and ouabain receptor of the myocardial sarcolemma in hypercholesterolemic rabbits. Male New Zealand white rabbits were fed with either standard chow or standard chow supplemented with 0.5% (w/w) cholesterol and 10% (w/w) coconut oil. After an 8 week feeding period, the rabbits underwent a thoracotomy and myocardial ischemia was induced by occlusion of the coronary artery. Myocardial samples from the ischemie and non-ischemic regions of the left ventricle of control and cholesterol-fed rabbits were taken for study. The cholesterol-fed group showed a decrease in both Na+-K+-ATPase activity and [3H]ouabain binding sites as compared to the control group. Ischemia caused a reduction in both Na+-K+ -ATPase activity and [3H]ouabain binding sites in both control and cholesterol-fed rabbits. The combination of ischemia and hypercholesterolemia produced an additive effect, with a further decrease in both Na+-K+-ATPase activity and [3H]ouabain binding sites. Neither the activity of Mg++-ATPase nor the binding affinity for [3H]ouabain was affected by either hypercholesterolemia or ischemia. These findings indicate that hypercholesterolemia may exaggerate certain aspects of functional deterioration arising during myocardial ischemia.