Numerous Classes of General Anesthetics Inhibit Etomidate Binding to γ-Aminobutyric Acid Type A (GABAA) Receptors
Numerous Classes of General Anesthetics Inhibit Etomidate Binding to γ-Aminobutyric Acid Type A (GABAA) Receptors
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DOI：
10.1074/jbc.m109.074708
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发表时间：
2010-03-19
影响因子：
4.8
通讯作者：
Olsen, Richard W.
中科院分区：
文献类型：
--
作者：
Li, Guo-Dong;Chiara, David C.;Olsen, Richard W.
增强γ-氨基丁酸A型受体(GABA(A)R)介导的抑制是大多数普通麻醉药的特性，也是麻醉分子机制的候选之一。静脉麻醉药，包括依托咪酯、异丙酚、巴比妥酸盐和神经活性类固醇，以及挥发性麻醉剂和长链醇，都在麻醉浓度下增强GABA(A)R功能。利用光亲和标记技术，在GABA(A)R跨膜区的β-α亚基界面上鉴定了依托咪酯的结合位点，从而支持了麻醉剂在GABA(A)R蛋白上存在受体位点的暗示；依托咪酯类似物[H-3]氮咪酯以药理学特定的方式标记了两个氨基酸，M1螺旋中的α1Met-236和M3螺旋中的βMet-286(Li，G.D.，Chiara，D.C.，Sawyer，G.W.，Husain，S.，Olsen，R.W.和Cohen，J.B.(2006)J.Neurosci)。26、11599-11605)。在这里，我们使用牛脑GABA(A)受体的[H-3]氮咪酯光标记来确定其他结构类别的麻醉药是否与依托咪酯结合部位相互作用。低毫摩尔浓度的异丙酚、巴比妥酸盐和挥发剂异氟醚对光标记有抑制作用，但辛醇和乙醇不能抑制光标记。药物特异性和立体特异性的巴比妥酸盐和异丙酚仅部分抑制，与变构相互作用一致，而异氟醚的抑制几乎完全，显然是竞争性的。蛋白质序列分析显示，异丙酚对α-1Met-236和β-Met-286的光标记有相同程度的抑制作用。这些结果表明，几类全身麻醉药调节依托咪酯与GABA(A)R的结合：异氟烷以毫米级亲和力直接结合到部位，而异丙酚和巴比妥酸盐抑制结合，但不以相互排斥的方式与依托咪酯结合。
Enhancement of gamma-aminobutyric acid type A receptor (GABA(A)R)-mediated inhibition is a property of most general anesthetics and a candidate for a molecular mechanism of anesthesia. Intravenous anesthetics, including etomidate, propofol, barbiturates, and neuroactive steroids, as well as volatile anesthetics and long-chain alcohols, all enhance GABA(A)R function at anesthetic concentrations. The implied existence of a receptor site for anesthetics on the GABA(A)R protein was supported by identification, using photoaffinity labeling, of a binding site for etomidate within the GABA(A)R transmembrane domain at the beta-alpha subunit interface; the etomidate analog [H-3]azietomidate photolabeled in a pharmacologically specific manner two amino acids, alpha 1Met-236 in the M1 helix and beta Met-286 in the M3 helix (Li, G. D., Chiara, D. C., Sawyer, G. W., Husain, S. S., Olsen, R. W., and Cohen, J. B. (2006) J. Neurosci. 26, 11599-11605). Here, we use [H-3]azietomidate photolabeling of bovine brain GABA(A)Rs to determine whether other structural classes of anesthetics interact with the etomidate binding site. Photolabeling was inhibited by anesthetic concentrations of propofol, barbiturates, and the volatile agent isoflurane, at low millimolar concentrations, but not by octanol or ethanol. Inhibition by barbiturates, which was pharmacologically specific and stereospecific, and by propofol was only partial, consistent with allosteric interactions, whereas isoflurane inhibition was nearly complete, apparently competitive. Protein sequencing showed that propofol inhibited to the same extent the photolabeling of alpha 1Met-236 and beta Met-286. These results indicate that several classes of general anesthetics modulate etomidate binding to the GABA(A)R: isoflurane binds directly to the site with millimolar affinity, whereas propofol and barbiturates inhibit binding but do not bind in a mutually exclusive manner with etomidate.