Open AccessAllosteric Interaction of Semotiadil Fumarate, a Novel Benzothiazine, with 1,4-Dihydropyridines, Phenylalkylamines, and 1,5-Benzothiazepines at the Ca2+-Channel Antagonist Binding Sites in Canine Skeletal Muscle Membranes
Author(s) -
Koichi Nakayama,
Yoshihisa Nozawa,
Yoshihisa Fukuta
Publication year - 1994
Publication title -
journal of cardiovascular pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.762
H-Index - 100
eISSN - 1533-4023
pISSN - 0160-2446
DOI - 10.1097/00005344-199405000-00007
Subject(s) - chemistry , dissociation constant , allosteric regulation , binding site , antagonist , diltiazem , stereochemistry , dihydropyridine , biophysics , ic50 , calcium channel , non competitive inhibition , calcium , biochemistry , enzyme , receptor , in vitro , biology , organic chemistry
We assessed the binding characteristics of a benzothiazine Ca(2+)-channel antagonist, semotiadil, in canine skeletal muscle membranes. Semotiadil inhibited binding of (+)-[3H]PN 200-110 (maximum inhibition 80%), and almost completely inhibited binding of both (-)-[3H]desmethoxyverapamil and D-cis-[3H]diltiazem to their specific binding sites with an IC50 value of 0.2-2 microM and a Hill slope of 0.6-0.9. Saturation isotherm and dissociation kinetic studies suggest that semotiadil acts as a noncompetitive inhibitor at the 1,4-dihydropyridine, phenylalkylamine, and benzothiazepine (BTZ) recognition sites in the L-type Ca2+ channel: (a) Scatchard analysis showed that semotiadil decreased maximum binding (Bmax) of the three classes of Ca2+ channel antagonists, while causing a slight increase in the equilibrium dissociation constant (Kd) in the case of (+)-[3H]PN 200-110 binding or no significant change in Kd values for binding of (-)-[3H]desmethoxyverapamil and D-cis-[3H]diltiazem to their specific binding sites; and (b) dissociation kinetics of the (+)-[3H]PN 200-110 and D-cis-[3H]diltiazem bindings were accelerated by semotiadil. These results suggest that semotiadil has a strong negative allosteric interaction with three classes of Ca2+ channel antagonists, including 1,4-dihydropyridines, phenylalkylamines, and BTZ at their specific binding sites.