Temperature-dependent modulation of [3H]nitrendipine binding by the calcium channel antagonists verapamil and diltiazem in rat brain synaptosomes.
Binding of the dihydropyridine calcium channel antagonist [3H]nitrendipine to an intact rat brain mitochondrial-synaptosomal fraction (P2) was specific, saturable, temperature-dependent and of high affinity (Kd = 115-467 pM). The effects of the calcium channel antagonists verapamil and diltiazem on [3H]nitrendipine binding and their temperature dependence were investigated. At 0 and 25 degrees C, verapamil inhibited [3H]nitrendipine binding incompletely in a manner consistent with an allosteric modulation and nearly independent of the incubation temperature. The effects of diltiazem, however, were found to be highly temperature-dependent. At 25 and 37 degrees C, 10 microM diltiazem enhanced [3H]nitrendipine binding to values of 140 and 200% of control, respectively. At 0 degrees C, 10 microM diltiazem inhibited [3H]nitrendipine binding to a value of 68% of control. Analysis of saturation isotherms at steady state demonstrated that at all temperatures studied the effects of verapamil and diltiazem on [3H]nitrendipine binding were due to alterations in the ligand dissociation constant (Kd). At 25 degrees C, these alterations were mediated by changes in the rate of ligand-receptor complex dissociation. Competition studies of verapamil and diltiazem at 25 and 0 degrees C indicate that the effects of these two drugs on [3H]nitrendipine binding are mutually exclusive. We conclude that the binding of [3H]nitrendipine is allosterically modulated by spacially related binding sites for verapamil and diltiazem.
D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism*; D004110:Diltiazem / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D066298:In Vitro Techniques; D008297:Male; D009543:Nifedipine / Q000031:analogs & derivatives* / Q000378:metabolism; D009568:Nitrendipine; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*; D013696:Temperature; D014316:Tritium; D014700:Verapamil / Q000494:pharmacology*
D001552:Benzazepines; D002121:Calcium Channel Blockers; D014316:Tritium; D009568:Nitrendipine; D014700:Verapamil; D004110:Diltiazem; D009543:Nifedipine