RT Journal Article SR Electronic T1 Selective modulation by membrane potential of desmethoxyverapamil binding to calcium channels in rat portal vein. JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 942 OP 947 VO 255 IS 3 A1 L Rakotoarisoa A1 I Sayet A1 C Mironneau A1 J Mironneau YR 1990 UL http://jpet.aspetjournals.org/content/255/3/942.abstract AB (-)-[3H]Desmethoxyverapamil (D888) binds saturably to intact strips from rat portal vein bathed in physiological solution with a Kd value of 363 pM and a maximal binding capacity value of 15.6 fmol.mg-1 wet weight. Unlabeled dihydropyridines, phenylalkylamines and benzothiazepines inhibited (-)-[3H]D888 specific binding in a concentration-dependent manner. Scatchard analyses and dissociation kinetics of (-)-[3H]D888 binding revealed the existence of mutual allosteric interactions between (+)-isradipine, (+)-cis diltiazem and (-)-D888 binding sites in portal vein strips. When voltage-dependent Ca++ channels transported Ca++, Ba++, Sr++ or Na+ the binding capacity of (-)-[3H]D888 remained unchanged. In contrast, both depolarization (induced by elevation of external K+) and hyperpolarization (in the presence of cromakalim) induced a gradual decrease in (-)-D888 binding capacity. These observations suggest that membrane potential variation would change the conformational state of Ca++ channels, in such a way that it would be less favorable for access of (-)-[3H]D888 to the binding site. This would provide an experimental argument in favor of the "guarded receptor hypothesis" according to which membrane potential modulates ligand affinity by alteration of the amount of time during which the receptor binding site is available to (-)-[3H]D888.