Increased Na+,K(+)-pump activity in erythrocytes of rabbits fed cholesterol.

Na+,L(+)-pump activity, intracellular sodium, potassium and magnesium concentrations and membrane cholesterol content were studied in erythrocytes of rabbits fed cholesterol. The average activity of the Na+,K(+)-pump in erythrocytes of rabbits with high plasma cholesterol was twice that in erythrocytes of control animals. Analysis showed a positive correlation between the pump activity and plasma cholesterol. The sodium content in erythrocytes correlated negatively with plasma cholesterol, as well as with the Na+,K(+)-pump activity. No significant differences in potassium and magnesium concentrations or in the membrane cholesterol content were observed between the two groups. The results indicate that modulation of the pump activity by cholesterol is not necessarily mediated by changes in the membrane viscosity.