van Swinderen B, Saifee O, Shebester L, Roberson R, Nonet M L, Crowder C M
Department of Anesthesiology, Division of Biology and Biomedical Sciences, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
Proc Natl Acad Sci U S A. 1999 Mar 2;96(5):2479-84. doi: 10.1073/pnas.96.5.2479.
The molecular mechanisms underlying general anesthesia are unknown. For volatile general anesthetics (VAs), indirect evidence for both lipid and protein targets has been found. However, no in vivo data have implicated clearly any particular lipid or protein in the control of sensitivity to clinical concentrations of VAs. Genetics provides one approach toward identifying these mechanisms, but genes strongly regulating sensitivity to clinical concentrations of VAs have not been identified. By screening existing mutants of the nematode Caenorhabditis elegans, we found that a mutation in the neuronal syntaxin gene dominantly conferred resistance to the VAs isoflurane and halothane. By contrast, other mutations in syntaxin and in the syntaxin-binding proteins synaptobrevin and SNAP-25 produced VA hypersensitivity. The syntaxin allelic variation was striking, particularly for isoflurane, where a 33-fold range of sensitivities was seen. Both the resistant and hypersensitive mutations decrease synaptic transmission; thus, the indirect effect of reducing neurotransmission does not explain the VA resistance. As assessed by pharmacological criteria, halothane and isoflurane themselves reduced cholinergic transmission, and the presynaptic anesthetic effect was blocked by the resistant syntaxin mutation. A single gene mutation conferring high-level resistance to VAs is inconsistent with nonspecific membrane-perturbation theories of anesthesia. The genetic and pharmacological data suggest that the resistant syntaxin mutant directly blocks VA binding to or efficacy against presynaptic targets that mediate anesthetic behavioral effects. Syntaxin and syntaxin-binding proteins are candidate anesthetic targets.
全身麻醉的分子机制尚不清楚。对于挥发性全身麻醉药（VAs），已发现脂质和蛋白质靶点的间接证据。然而，尚无体内数据明确表明任何特定的脂质或蛋白质与对临床浓度VAs的敏感性控制有关。遗传学提供了一种识别这些机制的方法，但尚未鉴定出强烈调节对临床浓度VAs敏感性的基因。通过对线虫秀丽隐杆线虫的现有突变体进行筛选，我们发现神经元 syntaxin 基因的突变可显性赋予对VAs异氟烷和氟烷的抗性。相比之下，syntaxin以及与syntaxin结合的蛋白突触小泡蛋白和SNAP-25中的其他突变则导致对VA的超敏反应。syntaxin的等位基因变异很显著，尤其是对于异氟烷，其敏感性范围可达33倍。抗性和超敏突变均会降低突触传递；因此，减少神经传递的间接作用并不能解释对VA的抗性。根据药理学标准评估，氟烷和异氟烷本身会降低胆碱能传递，而抗性syntaxin突变可阻断突触前麻醉作用。单个基因突变赋予对VAs的高水平抗性与麻醉的非特异性膜扰动理论不一致。遗传和药理学数据表明，抗性syntaxin突变体直接阻断VA与介导麻醉行为效应的突触前靶点的结合或作用效果。Syntaxin和与syntaxin结合的蛋白是潜在的麻醉靶点。
