(-)-[3H]Desmethoxyverapamil, a novel Ca2+ channel probe. Binding characteristics and target size analysis of its receptor in skeletal muscle

FEBS Lett. 1984 Oct 29;176(2):371-7. doi: 10.1016/0014-5793(84)81199-0.


(-)-[3H]Desmethoxyverapamil (2,7-dimethyl-3-(3,4-dimethoxyphenyl)-3-cyan- 7-aza-9-(3-methoxyphenyl)-nonanhydrochloride) was used to label putative Ca2+ channels in guinea pig skeletal muscle. The binding sites for (-)-[3H]desmethoxyverapamil co-purified with t-tubule membrane markers in an established subcellular fractionation procedure. (-)-[3H]Desmethoxyverapamil bound to partially purified t-tubule membranes with a KD of 2.2 +/- 0.1 nM and a Bmax of 18 +/- 4 pmol/mg membrane protein at 25 degrees C. Binding was stereoselectively inhibited by phenylalkylamine Ca2+ antagonists and in a mixed, non-competitive fashion by the benzothiazepine Ca2+ antagonist d-cis-diltiazem and the 1,4-dihydropyridine Ca2+ antagonist (+)-PN 200-110. Target size analysis of the (-)-[3H]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-[3H]diltiazem, was 130.5 +/- 4 kDa (p less than 0.01) and of the 1,4-dihydropyridine binding site 179 kDa, when labelled with [3H]nimodipine. It is concluded that (-)-[3H]desmethoxyverapamil is an extremely useful radioligand for the phenylalkylamine-selective receptor site of the t-tubule localized Ca2+ channel which is allosterically linked to two other distinct drug receptor sites.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Calcium / metabolism*
  • Diltiazem / metabolism
  • Guinea Pigs
  • Ion Channels / metabolism*
  • Kinetics
  • Muscles / metabolism*
  • Nicotinic Acids / metabolism
  • Nimodipine
  • Stereoisomerism
  • Subcellular Fractions / metabolism
  • Verapamil / analogs & derivatives*
  • Verapamil / metabolism


  • Ion Channels
  • Nicotinic Acids
  • Nimodipine
  • 4-desmethoxyverapamil
  • Verapamil
  • Diltiazem
  • Calcium