Interference of sodium with [3H]-nitrendipine binding to cardiac membranes

Interference of sodium with [3H]-nitrendipine binding was studied on membrane homogenates from guinea-pig skeletal muscle, cerebral cortex and left cardiac ventricle. [3H]-nitrendipine binding on homogenates from cerebral cortex and skeletal muscle was unaffected by Na+ (35 and 140 mEql(-1]. On the other hand, for the myocardial receptors, addition of Na+ resulted in an increase in IC50 of nitrendipine. Simultaneously, for the myocardial preparations, saturation curves showed a decrease in [3H]-nitrendipine affinity and an increase in the number of binding sites.