Circulation Research, Vol 64, 338-351, Copyright © 1989 by American Heart Association

ARTICLES

Voltage- and use-dependent modulation of cardiac calcium channels by the dihydropyridine (+)-202-791

TJ Kamp, MC Sanguinetti and RJ Miller
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.

The modulation of L-type voltage sensitive calcium channels in isolated guinea pig ventricular myocytes by the dihydropyridine (+)-202-791 was examined with the whole-cell voltage-clamp technique with 1.8 mM Ba or Ca as the charge carrier. Striking voltage- and use-dependent effects of the dihydropyridine calcium channel "agonist" (+)-202-791 were revealed. From a holding potential of -60 mV, depolarizing test pulses in the presence of (+)-202-791 demonstrated a concentration-dependent (EC50, 177 nM) increase in the measured peak inward barium current compared to control. In contrast, more depolarized holding potentials (greater than or equal to -30 mV) (+)-202-791 caused a biphasic effect on the peak inward current resulting in a transient enhancement followed by a steady-state block. A saturable, concentration-dependent hyperpolarizing shift in the voltage dependence of current inactivation was observed in the presence of (+)-202-791 with an EC50 of 10.2 nM. The voltage dependence of current activation was also shifted in the hyperpolarizing direction in the presence of (+)-202-791. A use- dependent relative block by (+)-202-791 was observed after repetitive depolarizing test pulses at a frequency of 2 Hz. Thus, the single enantiomer (+)-202-791 can result in either an increase in the whole cell calcium channel current (favored by hyperpolarized holding potentials and low rates of stimulation) or block of calcium channel current (favored by depolarized holding potentials and high rates of stimulation). Various combinations of (-)-202-791, a reported calcium channel antagonist, and (+)-202-791 resulted in intermediate effects on voltage sensitive calcium or barium currents compared with the presence of either enantiomer alone, and no clear cooperative interactions between the enantiomers were observed in contrast to a previous single channel study (Kokuban S, Prod'ham B, Becker C, Porzig H, Reuter H: Studies on Ca channels in intact cardiac cells: Voltage-dependent effects and cooperative interaction of dihydropyridine enantiomers. Mol Pharmacol 1986;30:571-584). The results are discussed in relation to the possible presence of multiple dihydropyridine receptors associated with the voltage sensitive calcium channel.

This article has been cited by other articles:

				A. Zahradnikova, I. Minarovic, and I. Zahradnik Competitive and Cooperative Effects of Bay K8644 on the L-Type Calcium Channel Current Inhibition by Calcium Channel Antagonists J. Pharmacol. Exp. Ther., August 1, 2007; 322(2): 638 - 645. [Abstract] [Full Text] [PDF]

				T. Sagawa, M. Nishio, K. Sagawa, J. E. Kelly, A. J. Lokuta, J. Tsai, E. Kan, and J. A. Wasserstrom Activation of purified cardiac ryanodine receptors by dihydropyridine agonists Am J Physiol Heart Circ Physiol, March 1, 2001; 280(3): H1201 - H1207. [Abstract] [Full Text] [PDF]

				C. Arnoult, M. Villaz, and H. M. Florman Pharmacological Properties of the T-Type Ca2+ Current of Mouse Spermatogenic Cells Mol. Pharmacol., June 1, 1998; 53(6): 1104 - 1111. [Abstract] [Full Text]

				M. J. Sinnegger, Z. Wang, M. Grabner, S. Hering, J. Striessnig, H. Glossmann, and J. Mitterdorfer Nine L-type Amino Acid Residues Confer Full 1,4-Dihydropyridine Sensitivity to the Neuronal Calcium Channel alpha 1A Subunit. ROLE OF L-TYPE MET1188 J. Biol. Chem., October 31, 1997; 272(44): 27686 - 27693. [Abstract] [Full Text] [PDF]

				I. Bodi, H. Yamaguchi, M. Hara, M. He, A. Schwartz, and G. Varadi Molecular Studies on the Voltage Dependence of Dihydropyridine Action on L-type Ca2+ Channels. CRITICAL INVOLVEMENT OF TYROSINE RESIDUES IN MOTIF IIIS6 AND IVS6 J. Biol. Chem., October 3, 1997; 272(40): 24952 - 24960. [Abstract] [Full Text] [PDF]

				M. C. Sanguinetti, J. H. Johnson, L. G. Hammerland, P. R. Kelbaugh, R. A. Volkmann, N. A. Saccomano, and A. L. Mueller Heteropodatoxins: Peptides Isolated from Spider Venom that Block Kv4.2 Potassium Channels Mol. Pharmacol., March 1, 1997; 51(3): 491 - 498. [Abstract] [Full Text] [PDF]