DIETARY-CHOLESTEROL AFFECTS NA-K+ PUMP FUNCTION IN RABBIT CARDIAC MYOCYTES()

Alterations in membrane cholesterol induced in vitro can alter Na+-Kpump function. Because dietary cholesterol can influence membrane chol esterol in vivo, we examined if dietary cholesterol is a determinant o f Na+-K+ pump function. Rabbits were fed cholesterol-supplemented diet s for 1-4 wk. Cardiac myocytes were then isolated, and Na+-K+ pump cur rents (I-p) were measured using the whole cell patch-clamp technique. When the Na+ concentration in the patch pipettes ([Na](pip)) was 10 mM , a modest diet-induced increase in serum cholesterol was associated w ith stimulation of I-p; large increases in serum cholesterol were asso ciated with inhibition. There was no effect of modest or large increas es in serum cholesterol on I-p when [Na](pip) was 80 mM. The [Na](pip) -I-p relationship determined using seven different levels of [Na](pip) from 0 to 80 mM indicated that a modest increase in serum cholesterol increased the apparent affinity of the pump for cytoplasmic Na+. In c ontrast, dietary cholesterol had no effect on the apparent affinity of the pump for extracellular K+. We conclude that cholesterol intake in fluences the sarcolemmal Na+-K+ pump. This may have clinical implicati ons for cardiovascular function.