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(—)‐[ 3 H]Desmethoxyverapamil, a novel Ca 2+ channel probe
Author(s) -
Goll A.,
Ferry D.R.,
Striessnig J.,
Schober M.,
Glossmann H.
Publication year - 1984
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(84)81199-0
Subject(s) - chemistry , radiochemistry , channel (broadcasting) , analytical chemistry (journal) , physics , chromatography , computer science , telecommunications
(—)‐[ 3 H]Desmethoxyverapamil (2,7‐dimethyl‐3‐(3,4‐dimethoxyphenyl)‐3‐cyan‐7‐aza‐9‐(3‐methoxyphenyl)‐nonanhydrochloride) was used to label putative Ca 2+ channels in guinea pig skeletal muscle. The binding sites for (—)‐[ 3 H]desmethoxyverapamil co‐purified with t‐tubule membrane markers in an established subcellular fractionation procedure. (—)‐[ 3 H]Desmethoxyverapamil bound to partially purified t‐tubule membranes with a K D of 2.2 ± 0.1 nM and a B max of 18 ± 4 membrane protein at 25°C. Binding was stereoselectively inhibited by phenylalkylamine Ca 2+ antagonists and in a mixed, non‐competitive fashion by the benzoihiazepine Ca 2+ antagonist d‐ cis ‐diltiazem and the 1,4‐dihydropyridine Ca 2+ antagonist (+)‐PN 200‐110. Target size analysis of the (—)‐[ 3 H]desmethoxyverapamil drug receptor site revealed a molecular mass of 107 ± 2 kDa. In contrast, the target size of the allosterically coupled benzothiazepine drug receptor site, labelled by d‐ cis ‐[ 3 H]diltiazem, was 130.5 ± 4 kDa ( p <0.01) and of the 1,4‐dihydropyridine binding site 179 kDa, when labelled with [ 3 H]nimodipine. It is concluded that (—)‐[ 3 H]desmethoxyverapamil is an extremely useful radioligand for the phenylalkylamine‐selective receptor site of the t‐tubule localized Ca 2+ channel which is allosterically linked to two other distinct drug receptor sites.