Changes in sarcolemmal K+ -p-nitrophenylphosphatase activity induced by atherogenic cholesterol--rapeseed oil diet in rabbit myocardium.

A high level of plasma lipids may possibly modify the composition and function of cardiac cell membranes and the activity of membrane-bound enzymes. Therefore, the activity of K+ -p-nitrophenylphosphatase (pNPPase) as a part of the Na+ -K+ ATPase was determined in myocardial homogenates to indicate sarcolemmal function after an atherogenic diet. After feeding of a cholesterol--rapeseed oil diet, the total and ouabain-sensitive activities of pNPPase were decreased significantly compared with controls. This decrease in pNPPase activity can be reproduced completely by a pure cholesterol diet. A rapeseed oil diet increases the total and ouabain-insensitive activity of pNPPase. Changes in enzyme activity may be caused by alterations in the lipid surroundings of this membrane-bound enzyme. The inhibition of pNPPase activity by 10(-6) M ouabain was smaller after cholesterol--rapeseed oil and pure cholesterol diets but greater after a pure oil diet. This indicates changes in ouabain sensitivity of pNPPase after various lipid diets.