Purified calcium channels have three allosterically coupled drug receptors

FEBS Lett. 1986 Mar 3;197(1-2):204-10. doi: 10.1016/0014-5793(86)80327-1.

Abstract

(-)-[3H]Desmethoxyverapamil and (+)-[3H]PN 200-110 were employed to characterize phenylalkylamine-selective and 1,4-dihydropyridine-selective receptors on purified Ca2+ channels from guinea-pig skeletal muscle t-tubules. In contrast to the membrane-bound Ca2+ channel, d-cis-diltiazem (EC50 = 4.5 +/- 1.7 microM) markedly stimulated the binding of (+)-[3H]PN 200-110 to the purified ionic pore. In the presence of 100 microM d-cis-diltiazem (which binds to the benzothiazepine-selective receptors) the Bmax for (+)-[3H]PN 200-110 increased from 497 +/- 81 to 1557 +/- 43 pmol per mg protein, whereas the Kd decreased from 8.8 +/- 1.7 to 4.7 +/- 1.8 nM at 25 degrees C. P-cis-Diltiazem was inactive. (-)-Desmethoxyverapamil, which is a negative heterotropic allosteric inhibitor of (+)-[3H]IN 200-110 binding to membrane-bound channels, stimulated 1,4-dihydropyridine binding to the isolated channel. (-)-[3H]Desmethoxyverapamil binding was stimulated by antagonistic 1,4-dihydropyridines [(+)-PN 200-110 greater than (-)(R)-202-791 greater than (+)(4R)-Bay K 8644] whereas the agonistic enantiomers (+)(S)-202-791 and (-)(4S)-Bay K 8644 were inhibitory and (-)-PN 200-110 was inactive. The results indicate that three distinct drug-receptor sites exist on the purified Ca2+ channel, two of which are shown by direct labelling to be reciprocally allosterically coupled.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
  • Allosteric Regulation
  • Amines / metabolism
  • Animals
  • Calcium / metabolism*
  • Calcium Channel Blockers
  • Dihydropyridines*
  • Diltiazem / pharmacology
  • Guinea Pigs
  • Ion Channels / drug effects
  • Ion Channels / metabolism*
  • Isradipine
  • Muscles / ultrastructure*
  • Nifedipine / analogs & derivatives
  • Nifedipine / pharmacology
  • Oxadiazoles / metabolism
  • Oxadiazoles / pharmacology
  • Pyridines / metabolism*
  • Pyridines / pharmacology
  • Receptors, Drug / metabolism*
  • Verapamil / analogs & derivatives
  • Verapamil / metabolism
  • Verapamil / pharmacology

Substances

  • Amines
  • Calcium Channel Blockers
  • Dihydropyridines
  • Ion Channels
  • Oxadiazoles
  • Pyridines
  • Receptors, Drug
  • 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
  • 1,4-dihydropyridine
  • 4-desmethoxyverapamil
  • Verapamil
  • Diltiazem
  • Nifedipine
  • Calcium
  • Isradipine