[3H] verapamil binding sites in skeletal muscle tranverse tubule membranes

³H]verapamil binding to muscle tubule membrane has the following properties. K_D = 27 ± 5 nM and maximum binding capacity B_max = 50 ± 5 pmol/mg of protein. A 1 = 1 stoichiometry of binding was found for the ratio of ³H]verapamil versus ³H] nitrendipine binding sites. The dissociation constant found at equilibrium is near that determined from the ratio of the rate constants for association (k₁) and dissociation (k_?1). Antiarrhythmic drugs like D600, diltiazem and bepridil are competitive inhibitors of ³H]verapamil binding with K_D values between 40 and 200 nM. Dihydropyridine analogs are apparent non competitive inhibitors of ³H]verapamil binding with half-maximum inhibition values (K_0.5) between 1 and 5 nM.