Molecular mechanisms of gaseous anesthetics on glutamate receptors : Identification of action site and examination of anesthetic behaviors in knock-out mice

研究了气体麻醉剂对配体门控离子通道的影响。一氧化二氮（0.58大气压（atm））和氙（0.46大气压）对各种受体表现出非常相似的作用。气态麻醉药对甘氨酸和GABA_A受体的增强作用远小于异氟醚，而氧化亚氮则抑制GABA_C受体。谷氨酸受体的抑制气体麻醉剂比异氟烷更明显，但小于乙醇。NMDA受体是谷氨酸受体中最敏感的，并被一氧化二氮抑制31%。氧化亚氮对5-HT_3受体有轻度抑制作用。烟碱性乙酰胆碱（nACh）受体的抑制气体和挥发性麻醉药，但乙醇加强他们。α4β2和α4β2 nACh受体的敏感性不同; α4β2受体被N2 O抑制是非竞争性的，并且对NMDA受体的依赖性略有不同，但对nACh受体没有影响。嵌合和点突变大鼠nAChRs的结果表明，第二跨膜段中间附近的单个氨基酸残基（β2-V253或β4-F255）决定了气态麻醉剂的敏感性。β亚基和α4亚基的同源残基（α4-V254）中该残基的突变表明，该位置也决定了n AChR对乙酰胆碱、异氟烷、戊巴比妥和己醇的敏感性。对ε2和ε 1 NMDA受体亚基的定点突变表明，ε 1亚基第二疏水段M2中保守的天冬酰胺残基决定了NMDA受体对气态麻醉剂的敏感性。

The effects of gaseous anesthetics on ligand-gated ion channels were investigated. Nitrous oxide (0.58 atmosphere (atm)) and xenon (0.46 atm) exhibited quite similar effects on various receptors. Glycine and GABA_A receptors were potentiated by gaseous anesthetics much less than by isoflurane, while nitrous oxide inhibited GABA_C receptors. Glutamate receptors were inhibited by gaseous anesthetics more markedly than by isoflurane, but less than by ethanol. NMDA receptors were the most sensitive among glutamate receptors, and were inhibited by nitrous oxide by 31%. 5-HT_3 receptors were slightly inhibited by nitrous oxide. The nicotinic acetylcholine (nACh) receptors were inhibited by gaseous and volatile anesthetics, but ethanol potentiated them. The sensitivity was different between α4β2 and α4β2 n ACh receptors ; α4β2 receptors were inhibited by nitrous oxide was non-competitive, and was slightly different depending on membrane potentials for NMDA receptors, but not for nACh receptors. The results of chimeric and point mutant rat nAChRs suggest that a single amino acid residue (β2-V253 or β4-F255) near the middle of the second transmembrane segment determines gaseous anesthetic sensitivity. Mutations of this residue in β subunits and the homologous residue of α4 subunits (α4-V254) showed that this position also determines sensitivities of n AChRs to acetylcholine, isoflurane, pentobarbital, and hexanol. The site-directed mutagenesis of ε2 and ζ1 NMDA receptor subunits showed that the conserved asparagine residue in the second hydrophobic segment M2 of the ζ1 subunit determines gaseous anesthetic sensitivity of NMDA receptors.