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 (K(d) = 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°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°C, 10 μM diltiazem enhanced [3H]nitrendipine binding to values of 140 and 200% of control, respectively. At 0°C, 10 μM 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 (K(d)). At 25°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°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.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Jan 1 1984|
ASJC Scopus subject areas
- Molecular Medicine