CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Slowed N-type calcium channel (CaV2.2) deactivation by the cyclin-dependent kinase inhibitor Roscovitine
Zafir Buraei 1, Mircea Anghelescu 2 and Keith S Elmslie 1*
1 Tulane University Health Sciences Center
2 University of South Alabama
* To whom correspondence should be addressed. E-mail: kelmslie{at}tulane.edu.
Submitted on September 14, 2004
Revised on November 22, 2004
Accepted on 26 May 2005
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Abstract |
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The lack of a calcium channel agonist (e.g. BayK8644) for CaV2 channels has impeded their investigation. Roscovitine, a potent inhibitor of cyclin-dependent kinases (cdk) 1, 2 & 5, has recently been reported to slow the deactivation of P/Q-type calcium channels (CaV2.1). We show that roscovitine also slows deactivation (EC50 ~ 53 µM) of N-type calcium channels (CaV2.2) and investigate gating alterations induced by roscovitine. The onset of slowed deactivation was rapid (~ 2 sec), which contrasts with a slower effect of roscovitine to inhibit N-current (EC50 ~300 µM). Slow deactivation was specific to roscovitine since it could not be induced by a closely related cdk inhibitor, olomoucine (300 µM). Intracellularly applied roscovitine failed to slow deactivation, which implies an extracellular binding site. The roscovitine-induced slow deactivation was accompanied by a slight left shift in the activation vs. voltage relationship, slower activation at negative potentials, and increased inactivation. Additional data showed that roscovitine preferentially binds to the open channel to slow deactivation. A model where roscovitine reduced a backward rate constant between two open states was able to reproduce the effect of roscovitine on both activation and deactivation.
Key Words:
Bullfrog sympathetic neurons, kinetic model, open-closed transitions, whole-cell patch clamp
