title: High-affinity binding of [3H]DTZ323 to the diltiazem-binding site of L-type Ca2+ channels.
abstract: D-cis-[N-Methyl-3H]-3-(acetyloxy)-5-[2-[[2-(3,4-dimethoxyphenyl)ethyl]-methylamino]ethyl]-2,3-dihydro-2-(4-methoxyphenyl)-1,5-benzothiazepine-4(5H)-one ([3H]DTZ323), a novel 1,5-benzothiazepine radioligand, was characterized in a ligand-receptor binding study. Specific binding of [3H]DTZ323 to rabbit skeletal muscle T-tubule membranes was saturable and reversible. Scatchard analysis indicated a single binding site with a K(d) value of 1.4 and 1.8 nM at 25 and 37 degrees C, respectively. DTZ323 and diltiazem derivatives inhibited specific [3H]DTZ323 binding with a rank order of DTZ323>DTZ417 (quaternary ammonium derivative of DTZ323)>diltiazem>L-cis-DTZ323. The affinity of DTZ323 was 51 times higher than that of diltiazem. [3H]DTZ323 binding was also completely inhibited by verapamil and tetrandrine, thus revealing the unique nature of the diltiazem-binding site. Specific [3H]DTZ323 binding to crude guinea pig ventricular membranes was inhibited by diltiazem, DTZ323 and its derivatives with IC(50) values close to those previously reported for the blockade of L-type Ca(2+) channel currents. These results indicate that [3H]DTZ323 is a potent and selective radioligand for the diltiazem-binding site of L-type Ca(2+) channels.
authors.affiliation: Laboratory of Cell Signaling, Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Bunkyo, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Hagiwara
authors.forename: Satomi
authors.initials: S
authors.lastname: Adachi-Akahane
authors.forename: Taku
authors.initials: T
authors.lastname: Nagao
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D044182:Benzylisoquinolines / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D004110:Diltiazem / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009529:Nicardipine / Q000494:pharmacology; D011817:Rabbits; D011869:Radioligand Assay; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; C105375:DTZ 323; C009438:tetrandrine; D014700:Verapamil; D009529:Nicardipine; D004110:Diltiazem