Temperature-dependent modulation of (/sup 3/H)nitrendipine binding by the calcium channel antagonists verapamil and diltiazem in rat brain synaptosomes
Binding of the dihydropyridine calcium channel antagonist (/sup 3/H)nitrendipine to an intact rat brain mitochondrial-synaptosomal fraction (P/sub 2/) was specific, saturable, temperature-dependent and of high affinity (K/sub d/ . 115-467 pM). The effects of the calcium channel antagonists verapamil and diltiazem on (/sup 3/H)nitrendipine binding and their temperature dependence were investigated. At 0 and 25 degrees C, verapamil inhibited (/sup 3/H)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 (/sup 3/H)nitrendipine binding to values of 140 and 200% of control, respectively. At 0 degrees C, 10 microM diltiazem inhibited (/sup 3/H)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 (/sup 3/H)nitrendipine binding were due to alterations in the ligand dissociation constant (K/sub d/). 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 (/sup 3/H)nitrendipine binding are mutually exclusive. We conclude that the binding of (/sup 3/H)nitrendipine is allosterically modulated by spacially related binding sites for verapamil and diltiazem.
- Research Organization:
- Department of Pharmacology, University of Arizona Health Sciences Center, Tucson
- OSTI ID:
- 7017071
- Journal Information:
- J. Pharmacol. Exp. Ther.; (United States), Vol. 229:2
- Country of Publication:
- United States
- Language:
- English
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