Pharmacologic and radioligand binding studies of 1,4-dihydropyridines in rat cardiac and vascular preparations: stereoselectivity and voltage dependence of antagonist and activator interactions

W Zheng, J Stoltefuss, S Goldmann and DJ Triggle

Department of Biochemical Pharmacology, School of Pharmacy, State University of New York, Buffalo 14260.

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.

Volume 41, Issue 3, pp. 535-541, 03/01/1992
Copyright © 1992 by American Society for Pharmacology and Experimental Therapeutics

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