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

[3H]verapamil binding to muscle tubule membrane has the following properties. KD = 27 +/- 5 nM and maximum binding capacity Bmax = 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 KD values between 40 and 200 nM. Dihydropyridine analogs are apparent non competitive inhibitors of [3H]verapamil binding with half-maximum inhibition values (K0.5) between 1 and 5 nM.