Characterization of a binding site of 「3 H」semotiadil fumarate, a novel benzothiazine Ca2+ antagonis, in rabbit skeletal muscle membranes

• Published in: Japanese Journal of Pharmacology 1995, Vol.67 (suppl.1), p.96-96
• Main Authors: Daisuke Shii, Nobuaki Miyawaki, Katsuhiko Nakata, Koichi Nakayama
• Format: Article
• Language: Japanese
• ISSN: 0021-5198

The present study was undertaken to investigate the binding properties of 「^^3 H」semotiadil in rabbit skeletal muscle membranes. 「^^3 H」Semotiadil had a single class of high affinity binding site (Kd=21.6nM. Bmax=6.26 pmol/mg protein, N_H =0.94) in rabbit skeletal muscle membranes. The association and dissociation of the specific binding of 「^^3 H」semotiadil to the Ca^2+ channel were very rapid. The bind ing was inhibited by SD-3212, S-enantiomer of semotiadil, with a higher Ki(Ki=298.0nM) than semotiadil(Ki=38.6nM), and the speciflc 「^^3 H」semotiadil binding increased under low temperature condition. The specific binding of 「^^3 H」semotiadil was completely inhibited by diltiazem(Ki=368.5nM) and verapamil (Ki=150.7nM). Nifedipine showed a tendency to increase the binding of 「^^3 H」semotiadil. The specific binding of 「^^3 H」semotiadil was hardly affected by CaCl_2 up to 10mM. It has been already reported that unlabeled semotiadil allosterically interacts with the binding sites of (+)-「^^3 H」PN200-110, d-cis-「^^3 H」diltiazem and (-)-「^^3 H」desmethoxyverapamil. Taken together, it is suggested that a high affinity binding site of semotiadil exists on L-type Ca^2+ channels in rabbit skeletal muscle membranes, which may be different from the three well-characterized binding sites of 1,4-dihydropyridines, benzothiazepines and phenylalkylamines.