Received for publication February 17, 2006.
Revised April 26, 2006.
Accepted for publication May 12, 2006.

State-dependent verapamil block of the cloned human Ca_V3.1 T-type Ca²⁺ channel

Abstract

Verapamil is a potent phenylalkylamine antihypertensive thought to exert its therapeutic effect primarily by blocking high-voltage activated L-type calcium channels. It was the first clinically used calcium channel blocker and remains in clinical use, although it has been eclipsed by other calcium channel blockers because of its short half-life and interactions with other channels. In addition to blocking L-type channels, it has been reported to block T-type (low-voltage activated) calcium channels. This type of cross-reactivity is likely to be beneficial in the effective control of blood pressure. Although the interactions of T-channels with a number of drugs have been described, the mechanisms by which these agents modulate channel activity are largely unknown. Most calcium channel blockers exhibit state-dependence, i.e. preferential binding to certain channel conformations, but little is known about state-dependent verapamil block of T-channels. We stably expressed human Ca_V3.1 T-type channels in HEK-293 cells and studied the state-dependence of the drug with macroscopic and gating currents. Verapamil blocked currents at similar micromolar concentrations at polarized potentials as reported for L-type channels, although unlike for L-type currents, it did not affect current time course. The drug exhibited use-dependence and significantly slowed the apparent recovery from inactivation. Current inhibition was dependent on potential. This dependence was restricted to negative potentials, although all data were consistent with verapamil binding in the pore. Gating currents were unaffected by verapamil. We propose that verapamil achieves its inhibitory effect via occlusion of the channel pore associated with an open/inactivated conformation of the channel.

Key words: Calcium (Votage-Gated Channels), Func. analysis receptor/ion channel mutants

This article has been cited by other articles:

				R. C. K. Cheng, D. B. Tikhonov, and B. S. Zhorov Structural Model for Phenylalkylamine Binding to L-type Calcium Channels J. Biol. Chem., October 9, 2009; 284(41): 28332 - 28342. [Abstract] [Full Text] [PDF]