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(+)−[ 3 H]‐PN 200–110 binding to cell membranes and intact strips of portal vein smooth muscle: characterization and modulation by membrane potential and divalent cations
Author(s) -
Dacquet C.,
Loirand G.,
Rakotoarisoa L.,
Mironneau C.,
Mironneau J.
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb11949.x
Subject(s) - chemistry , divalent , calcium , diltiazem , dissociation constant , membrane , biophysics , binding site , dihydropyridine , isradipine , membrane potential , stereochemistry , biochemistry , receptor , biology , organic chemistry
1 Specific binding of the calcium‐antagonist dihydropyridine derivative, (+)−[ 3 H]‐PN 200–110 (isradipine), to cell membranes of equine portal vein smooth muscle was compared with binding to intact strips isolated from rat portal veins. 2 Specific binding to vascular smooth muscle membranes was of high affinity, saturable and reversible. The dissociation constant obtained from association and dissociation kinetics of (+)−[ 3 H]‐PN 200–110 was similar to that obtained from equilibrium binding and competition experiments. 3 Specific binding of (+)−[ 3 H]‐PN 200–110 was completely displaced by unlabelled dihydropyridines. Among other calcium antagonists, D888 and (+)− cis ‐diltiazem partially inhibited the binding at 25°C. At 37°C, only (+)− cis ‐diltiazem stimulated the binding. LaCl 3 , CdCl 2 , NiCl 2 , CoCl 2 had inhibitory effects, whereas KCl and NaCl had no effect. 4 When intact strips of portal vein were incubated in high external potassium concentrations for 30 min, the K d was lowered to 0.04 ± 0.01 n m from the control value of 0.14 + 0.02 n m ( n = 5), thereby indicating that (+)−[ 3 H]‐PN 200–110 bound to voltage‐dependent calcium channels, with a higher affinity, in the depolarized state. 5 When external Ca 2+ was removed or substituted with Ba 2+ or Sr 2+ , K d values increased suggesting that the dihydropyridine binding to intact strips was modulated by binding of Ca 2+ ions to voltage‐dependent calcium channels.