Solubilization of the nitrendipine receptor from skeletal muscle transverse tubule membranes Interactions with specific inhibitors of the voltage‐dependent Ca 2+ channel

The nitrendipine receptor associated with the voltage‐dependent calcium channel from rabbit skeletal muscle transverse tubule membranes has been solubilized by detergent extraction. A highly stable solubilized receptor preparation was obtained using 3‐[(3‐cholamidopropyl)dimethyl‐ammonio]‐1‐propanesulfonate as detergent with phospholipids or glycerol present as stabilizing agents. Binding of [ 3 H]nitrendipine to the solubilized receptor was reversible and saturable. At 4°C the equilibrium dissociation constant of the [ 3 H]nitrendipine receptor complex was 7±3nM and was close to that determined from the rate constants of association ( k 1 = 1.3 10 5 M −1 s −1 ) and dissociation ( k −1 = 1.10 × 10 −3 s −1 ) of 8.4nM. The nitrendipine concentration that gave a half‐maximal inhibition of [ 3 H]nitrendipine binding to the solubilized receptor was 10 nM, which was similar to the values for the dissociation constant determined for the radiolabelled ligand. [ 3 H]Nitrendipine binding to its solubilized receptor was also inhibited by other antiarrythmic drugs, such as bepridil and verapamil, and enhanced by d‐cis ‐diltiazem. Since these drugs are apparent non‐competitive inhibitors of [ 3 H]nitrendipine binding it was concluded that these different binding sites are tightly coupled. Sucrose density sedimentation of solubilized nitrendipine receptor resulted in the separation of three [ 3 H]nitrendipine binding activities with apparent sedimentation coefficients of 11.4 S. 14.4 S and 21S.