NMDA channel gating is influenced by a tryptophan residue in the M2 domain but calcium permeation is not altered

D. P. Buck, S. M. Howitt, J. D. Clements*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    15 Citations (Scopus)

    Abstract

    N-Methyl-D-aspartate (NMDA) receptors are susceptible to open-channel block by dizolcipine (MK-801), ketamine and Mg2+ and are permeable to Ca2+. It is thought that a tryptophan residue in the second membrane-associated domain (M2) may form part of the binding site for open-channel blockers and contribute to Ca2+ permeability. We tested this hypothesis using recombinant wild-type and mutant NMDA receptors expressed in HEK-293 cells. The tryptophan was mutated to a leucine (W-5L) in both the NMDAR1 and NMDAR2A subunits. MK-801 and ketamine progressively inhibited currents evoked by glutamate, and the rate of inhibition was increased by the W-5L mutation. An increase in open channel probability accounted for the acceleration. Fluctuation analysis of the glutamate-evoked current revealed that the NMDAR1 W-5L mutation increased channel mean open time, providing further evidence for an alteration in gating. However, the equilibrium affinities of Mg2+ and ketamine were largely unaffected by the W-5L mutation, and Ca2+ permeability was not decreased. Therefore, the M2 tryptophan residue of the NMDA channel is not involved in Ca2+ permeation or the binding of open-channel blockers, but plays an important role in channel gating.

    Original languageEnglish
    Pages (from-to)2454-2462
    Number of pages9
    JournalBiophysical Journal
    Volume79
    Issue number5
    DOIs
    Publication statusPublished - 2000

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