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J. Biol. Chem., Vol. 279, Issue 6, 3990-3997, February 6, 2004

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How Fast Does the GluR1Q_flip Channel Open?^*

Gang Li and Li Niu

From the Department of Chemistry and the Center for Neuroscience Research, State University of New York, Albany, New York 12222

Opening of a ligand-gated ion channel is the step at which the binding of a neurotransmitter is transduced into the electrical signal by allowing ions to flow through the transmembrane channel, thereby altering the postsynaptic membrane potential. We report the kinetics for the opening of the GluR1Q_flip channel, an -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit of the ionotropic glutamate receptors. Using a laser-pulse photolysis technique that permits glutamate to be liberated photolytically from -O-(-carboxy-2-nitrobenzyl)glutamate (caged glutamate) with a time constant of 30 µs, we show that, after the binding of glutamate, the channel opened with a rate constant of (2.9 ± 0.2) x 10⁴ s^–1 and closed with a rate constant of (2.1 ± 0.1) x 10³ s^–1. The observed shortest rise time (20–80% of the receptor current response), i.e. the fastest time by which the GluR1Q_flip channel can open, was predicted to be 35 µs. This value is three times shorter than those previously reported. The minimal kinetic mechanism for channel opening consists of binding of two glutamate molecules, with the channel-opening probability being 0.93 ± 0.10. These findings identify GluR1Q_flip as one of the temporally efficient receptors that transduce the binding of chemical signals (i.e. glutamate) into an electrical impulse.

Received for publication, September 22, 2003 , and in revised form, November 5, 2003.

^* This work was supported in part by American Heart Association Grant 0130513T and by grants from the Amyotrophic Lateral Sclerosis Association and the Muscular Dystrophy Association (to L. N.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported by a postdoctoral fellowship from the Muscular Dystrophy Association.

To whom correspondence should be addressed: Dept. of Chemistry, SUNY, 1400 Washington Ave., Albany, NY 12222. Tel.: 518-442-4447; Fax: 518-442-3462; E-mail: lniu{at}albany.edu.

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