Pharmacologic and radioligand binding studies of 1,4-dihydropyridines in rat cardiac and vascular preparations: stereoselectivity and voltage dependence of antagonist and activator interactions.
The pharmacologic and radioligand-binding properties of 1,4-dihydropyridines in an activator (Bay K 8644) and an antagonist (nifedipine) series were studied in rat tail artery, heart membrane, and neonatal rat ventricular myocytes. The S-enantiomers of the activator series contracted rat tail artery in the presence of 15 mM K+ (EC50 values of 10(-8) to 10(-5) M). (S)-Bay K 8644 (I) and its o-difluoromethoxy analog (III) were the most potent members of the activator series examined. The abilities of the activators to stimulate maximum tension response of the artery differed with structure; thus, the efficacy of (S)-Bay K 8644 was 70% that of the analog lacking the 3-carbomethoxy group. The R-enantiomers of the activator series and a series of achiral nifedipine analogs were inhibitory in the same tissue. The intact-cell binding assay revealed the binding affinities of 1,4-dihydropyridine antagonists in depolarized cells (50 mM K+) to be higher than those in polarized cells (5 mM K+). The ratio KD (polarized)/KD (depolarized) was 77 for nifedipine (IC50 = 5.4 x 10(-9) M) but was only 2.9 for the weak 3-methoxy nifedipine analog (IC50 = 4.8 x 10(-6) M); an approximately linear relationship exists between this ratio and the antagonist potency. In marked contrast, and in confirmation of previous work [Mol. Pharmacol. 35:541-552 (1989)], the binding affinities of activators were not significantly affected by membrane potential, regardless of potency. We conclude that the S-enantiomers of Bay K 8644 analogs are activators with different potency and efficacy and that the R-enantiomers are antagonists, that the binding of 1,4-dihydropyridine antagonists is voltage dependent, whereas binding of the activators is not, and that the voltage-dependence of binding of the antagonists is correlated with the potency of the antagonist.
Department of Biochemical Pharmacology, School of Pharmacy, State University of New York, Buffalo 14260.
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Zheng
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Stoltefuss
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Goldmann
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Triggle
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects* / Q000502:physiology; D001667:Binding, Competitive; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004095:Dihydropyridines / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D004336:Drug Antagonism; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D017275:Isradipine; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats
D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D009543:Nifedipine; D017275:Isradipine