title: Alcohols inhibit N-methyl-D-aspartate receptors via a site exposed to the extracellular environment.
abstract: N-Methyl-D-aspartate (NMDA) receptors are important CNS target sites of alcohols, but the site and mechanism of action of alcohols on NMDA receptors remains unclear. In CHO-K1 cells transfected with NR1/NR2B NMDA receptor subunits, ethanol inhibited NMDA-activated current with an IC(50) of 138 mM. Truncation of the intracellular C-terminal domain of the NR1 subunit (NR1T) did not alter ethanol sensitivity when combined with the NR2B subunit, but a similar truncation of the NR2B subunit (NR2BT) slightly enhanced ethanol sensitivity of receptors formed from coexpression with either NR1 or NR1T subunits. 1-Pentanol applied externally inhibited NMDA receptors with an IC(50) of 9.9 mM, but intracellular application of 1-pentanol (25 mM) did not alter NMDA receptor inhibition by externally applied ethanol or 1-pentanol. In addition, the amplitude of NMDA-activated current did not decrease during the time required for 1-pentanol (25 mM) to diffuse throughout the cytoplasm. Ethanol did not inhibit NMDA receptors when bath-applied in cell-attached patches or when applied to the cytoplasmic face of inside-out membrane patches. These results appear to be best explained by an action of alcohols on the NMDA receptor-channel protein, at a site located in a domain exposed to, or only accessible from, the extracellular environment.
authors.affiliation: Unit on Cellular Neuropharmacology, Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 20892-8115, Bethesda, MD 20892-8115, USA. bpeoples@helix.nih.gov
authors.forename: R W
authors.initials: RW
authors.lastname: Peoples
authors.forename: R R
authors.initials: RR
authors.lastname: Stewart
mesh_terms: D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D000431:Ethanol / Q000494:pharmacology*; D005110:Extracellular Space; D005998:Glycine / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009154:Mutation; D016202:N-Methylaspartate / Q000494:pharmacology; D000439:Pentanols / Q000378:metabolism / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D008164:Luminescent Proteins; D000439:Pentanols; D016194:Receptors, N-Methyl-D-Aspartate; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000431:Ethanol; D016202:N-Methylaspartate; C024999:n-pentanol; D005998:Glycine