Open AccessCharacteristics of [3H]Nimodipine Binding to Sarcolemmal Membranes from Rat Vas Deferens and Its Regulation by Guanine Nucleotide
Author(s) -
Katsuya Higo,
Hiroshi Saito,
Norio Matsuki
Publication year - 1988
Publication title -
japanese journal of pharmacology/japanese journal of pharmacology
Language(s) - English
Resource type - Journals
eISSN - 1347-3506
pISSN - 0021-5198
DOI - 10.1254/jjp.48.213
Subject(s) - nimodipine , dissociation constant , diltiazem , verapamil , binding site , chemistry , vas deferens , dihydropyridine , biophysics , calcium , binding constant , calcium channel , stereochemistry , biochemistry , endocrinology , biology , receptor , organic chemistry
The binding properties of a 1,4-dihydropyridine (DHP) calcium entry blocker, [3H]nimodipine, to a microsomal fraction from rat vas deferens was characterized. The specific binding was saturable, rapid and reversible. Scatchard analysis of the binding revealed a single binding site, and the dissociation constant and the maximum number of binding sites were 0.31 +/- 0.02 nM and 97.0 +/- 7.19 fmol/mg protein, respectively. Both the Kd value obtained from the kinetic study and the IC50 value from relaxation of the K+-depolarized organ were approximately 0.4 nM, indicating that the binding site is closely related to the functional Ca2+ channel. The specific [3H]nimodipine binding was displaced by DHP derivatives at low concentration and by verapamil at high concentration, but diltiazem had no effect on the binding. Calcium chelating agents decreased the [3H]nimodipine binding which was restored by adding Ca2+. 5'-Guanylylimidodiphosphate caused a rightward shift of the displacement curve for Bay K 8644 but not for nimodipine, suggesting the involvement of guanine nucleotide binding protein in the signal transduction between the DHP binding site and the Ca2+ channel.