Sodium channel comodification with full activator reveals veratridine reaction dynamics

G Wang, M Dugas, BI Armah and P Honerjager

Institut fur Pharmakologie und Toxikologie, Technischen Universitat Munchen, FRG.

Veratridine association and dissociation rates were determined at single sodium channels in outside-out patches of cultured ventricular myocytes obtained from late-fetal rat hearts. In single cardiac sodium channels depolarized from -110 to -30 mV, intracellular veratridine induced a long lasting (tau = 0.48 sec) open state with small current amplitude (-0.3 pA, i.e., 1/4 of normal) and frequent closing transitions, giving it a burstlike appearance, in agreement with reports on other types of sodium channel. Veratridine-associated and veratridine-free states of a single sodium channel were monitored by comodifying it with an allosteric activator, BDF 9145 (1 microM), that induced a burst with normal open channel current amplitude (-1.2 pA at - 30 mV) upon veratridine dissociation. Veratridine and BDF 9145 interacted with reciprocal synergism at the single sodium channel such that veratridine-induced bursts (called P-bursts for partially activated) alternated with BDF 9145-induced bursts (called F-bursts for fully activated) many times following a single depolarization to -30 mV. P-bursts and F-bursts within such trains of bursts had exponentially distributed durations. The reciprocal time constant for F- bursts, tau F-1, increased linearly with veratridine concentration (0.3- 30 microM), whereas tau P was insensitive. We conclude, therefore, that P-bursts reflect veratridine occupancy and F-bursts reflect the veratridine-free state; if veratridine and BDF 9145 bind to a sodium channel simultaneously, veratridine exerts conformational dominance, i.e., retains its property to reduce channel conductance. For the single cardiac sodium channel activated (i.e., deprived of inactivation) by BDF 9145, we have determined a veratridine association rate constant k1 = 4.3 x 10(6) M0-1 sec-1, dissociation rate constant K- 1 = 2.2 sec-1 and equilibrium dissociation constant KD = 5.1 x 10(-7) M (20 degrees, -30 mV membrane potential).

Volume 37, Issue 2, pp. 144-148, 02/01/1990
Copyright © 1990 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				W. Ulbricht Sodium Channel Inactivation: Molecular Determinants and Modulation Physiol Rev, October 1, 2005; 85(4): 1271 - 1301. [Abstract] [Full Text] [PDF]

				M. R. Pelletier, P. A. Pahapill, P. S. Pennefather, and P. L. Carlen Analysis of Single KATP Channels in Mammalian Dentate Gyrus Granule Cells J Neurophysiol, November 1, 2000; 84(5): 2291 - 2301. [Abstract] [Full Text] [PDF]

				M. J. Little, C. Zappia, N. Gilles, M. Connor, M. I. Tyler, M.-F. Martin-Eauclaire, D. Gordon, and G. M. Nicholson delta -Atracotoxins from Australian Funnel-web Spiders Compete with Scorpion alpha -Toxin Binding but Differentially Modulate Alkaloid Toxin Activation of Voltage-gated Sodium Channels J. Biol. Chem., October 16, 1998; 273(42): 27076 - 27083. [Abstract] [Full Text] [PDF]