Neurotransmitter-gated membrane ion channels are among the most important target sites of alcohol action in the nervous system, although the manner in which alcohols modulate the function of these transmembrane proteins has not been established.
The aim of this project is to investigate the actions of alcohols and related compounds on neurotransmitter-gated ion channels thought to be involved in producing the intoxicating effects of alcohols in nervous tissue. Previous studies have shown that the function of the N-methyl-D- aspartate (NMDA) receptor-channel, a type of receptor for the excitatory neurotransmitter glutamate, is inhibited by intoxicating concentrations of ethanol. In addition, n-alcohols with 8 or fewer carbon atoms inhibit NMDA receptor-ion channel function, while larger n-alcohols do not. This cutoff effect was originally proposed to result from size-exclusion; i.e., alcohols act by binding to an amphiphilic region on the receptor-ion channel protein, and alcohols above the cutoff are unable to bind because their size exceeds the dimensions of the site. To test this hypothesis, the effects of a series of straight- chain 1,omega-diols, which have lower hydrophobicity but slightly greater molecular volume than the corresponding alcohols, were evaluated on NMDA-activated current in mammalian cells transfected with NR1/NR2B NMDA receptor subunits. These experiments revealed that diols with 9 or more carbon atoms were able to inhibit NMDA-activated current, despite having molecular volumes greater than those of the corresponding alcohols. This result suggests that the cutoff effect on NMDA receptor-ion channels most probably results from the inability of long-chain alcohols to achieve adequate concentrations at the site of action on the protein due to low aqueous solubility, rather than from a size-exclusion mechanism. Experiments were also performed to identify the location of the site of alcohol action on the NMDA receptor in mammalian cells transfected with NR1/NR2B NMDA receptor subunits. Intracellular application of 1-pentanol did not inhibit NMDA-activated current, and did not alter the inhibitory effect of extracellularly- applied ethanol or pentanol. Application of ethanol to the cytoplasmic face of inside-out membrane patches did not alter NMDA-activated current. In addition, the inhibitory effect of extracellularly-applied ethanol was not altered by truncation of the intracellular C-termini of both subunits. These results are consistent with an action of alcohols on the extracellular domain of the NMDA receptor-ion channel. - Alcohol Ion channel Glutamate NMDA Patch-clamp Primary culture Central Nervous System Transfection
| Kanemitsu, Yoshio; Hosoi, Masako; Zhu, Ping Jun et al. (2003) Dynorphin A inhibits NMDA receptors through a pH-dependent mechanism. Mol Cell Neurosci 24:525-37 |
| Yevenes, Gonzalo E; Peoples, Robert W; Tapia, Juan C et al. (2003) Modulation of glycine-activated ion channel function by G-protein betagamma subunits. Nat Neurosci 6:819-24 |
| Ren, Hong; Honse, Yumiko; Karp, Brian J et al. (2003) A site in the fourth membrane-associated domain of the N-methyl-D-aspartate receptor regulates desensitization and ion channel gating. J Biol Chem 278:276-83 |
| Peoples, Robert W; Ren, Hong (2002) Inhibition of N-methyl-D-aspartate receptors by straight-chain diols: implications for the mechanism of the alcohol cutoff effect. Mol Pharmacol 61:169-76 |
| Peoples, R W; Stewart, R R (2000) Alcohols inhibit N-methyl-D-aspartate receptors via a site exposed to the extracellular environment. Neuropharmacology 39:1681-91 |
