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

1 Interference of sodium with [3H]‐nitrendipine binding was studied on membrane homogenates from guinea‐pig skeletal muscle, cerebral cortex and left cardiac ventricle. 2 [3H]‐nitrendipine binding on homogenates from cerebral cortex and skeletal muscle was unaffected by Na+ (35 and 140 mEql−1). 3 On the other hand, for the myocardial receptors, addition of Na+ resulted in an increase in IC50 of nitrendipine. 4 Simultaneously, for the myocardial preparations, saturation curves showed a decrease in [3H]‐nitrendipine affinity and an increase in the number of binding sites.