A comparison between the binding and electrophysiological effects of dihydropyridines on cardiac membranes

SL Hamilton, A Yatani, K Brush, A Schwartz and AM Brown

To investigate the mechanism of action of dihydropyridines on calcium channels, both receptor binding and the electrophysiological effects of optically pure enantiomers of Bay k 8644, Sandoz 202-791, nimodipine, and PN200-110 were studied in a guinea pig ventricular preparation. The radioligand binding studies are consistent with other reports that the inhibitory and excitatory dihydropyridines share a single binding site. The patch clamp method was used for recording whole cell calcium currents. (-)-Bay k 8644 and (+)-202-791 produced voltage-dependent increases in the calcium currents. The magnitude of the effect was dependent on the holding potential. At holding potentials between -40 and -90 mV these activators increased calcium currents in a concentration-dependent manner with EC50 values of 25 nM and 80 nM, respectively. The inhibitors (+)-Bay k 8644, (-)-202-791, (+)- and (-)- nimodipine, and (+)-PN200-110 blocked the calcium currents with potencies that depended upon holding potential. The IC50 values for these enantiomers measured at a holding potential of -80 mV were, respectively, 8000, 200, 2000, 450, and 400 nM, and IC50 values measured at a holding potential of -30 mV were 26, 1.0, 52, 4.0, and 4.5 nM. The dissociation constants calculated for some dihydropyridines are similar to the Kd values determined by radioligand binding. However, for other dihydropyridines, large discrepancies between the concentrations giving rise to half-maximal electrophysiological effects and the Kd values from binding studies could not be reconciled by voltage-dependent binding alone. We suggest that each dihydropyridine also produces unique effects on the voltage-dependent gating of calcium channels.

Volume 31, Issue 3, pp. 221-231, 03/01/1987
Copyright © 1987 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				B. Z. Peterson and W. A. Catterall Allosteric Interactions Required for High-Affinity Binding of Dihydropyridine Antagonists to CaV1.1 Channels Are Modulated by Calcium in the Pore Mol. Pharmacol., August 1, 2006; 70(2): 667 - 675. [Abstract] [Full Text] [PDF]

				C. P. Ingalls, G. L. Warren, J.-Z. Zhang, S. L. Hamilton, and R. B. Armstrong Dihydropyridine and ryanodine receptor binding after eccentric contractions in mouse skeletal muscle J Appl Physiol, May 1, 2004; 96(5): 1619 - 1625. [Abstract] [Full Text] [PDF]

				S. Mitra, M. Ugur, O. Ugur, H. M. Goodman, J. R. McCullough, and H. Yamaguchi (S)-Albuterol Increases Intracellular Free Calcium by Muscarinic Receptor Activation and a Phospholipase C-Dependent Mechanism in Airway Smooth Muscle Mol. Pharmacol., March 1, 1998; 53(3): 347 - 354. [Abstract] [Full Text]

				A. Yatani, M. Wakamori, T. Niidome, S. Yamamoto, I. Tanaka, Y. Mori, K. Katayama, and S. Green Stable Expression and Coupling of Cardiac L-Type Ca2+ Channels With ß1-Adrenoceptors Circ. Res., March 1, 1995; 76(3): 335 - 342. [Abstract] [Full Text]