Siegwart Roberta, Jurd Rachel, Rudolph Uwe
Institute of Pharmacology and Toxicology, University of Zürich, Zürich, Switzerland.
J Neurochem. 2002 Jan;80(1):140-8. doi: 10.1046/j.0022-3042.2001.00682.x.
General anesthetics modulate the activity of ligand-gated ion channels including the GABA(A) receptor. Mutational studies mainly on the benzodiazepine-insensitive alpha(2)beta(1(M286W)) and alpha(6)beta(3(N289M))gamma(2) GABA(A) receptors revealed that a serine in transmembrane domain 2 and a methionine in transmembrane domain 3 are essential for the action of most general anesthetics. We investigated whether these residues would similarly be relevant for their action at the benzodiazepine-sensitive GABA receptor subtype, alpha(2)beta(3)gamma(2). We found that not only the N265M but also the M286W mutation nearly abolished the modulatory effect of etomidate. However, the anti-convulsant loreclezole, a structural homologue of etomidate, was inactive on the N265M mutant, but displayed normal modulatory activity on the M286W mutant. Both mutations did not affect the modulatory action of the neurosteroid alphaxalone. The direct action of alphaxalone, however, was dramatically increased in the M286W mutant to about twice the maximal GABA current but not significantly affected in the N265M mutant. These data demonstrate that the structural requirements for modulatory and direct actions of various general anesthetics are distinct. The molecular switches induced by these mutations can be exploited to identify the molecular determinants for the action of general anesthetics.
全身麻醉药可调节包括GABA(A)受体在内的配体门控离子通道的活性。主要针对苯二氮䓬不敏感的α(2)β(1(M286W))和α(6)β(3(N289M))γ(2) GABA(A)受体的突变研究表明，跨膜结构域2中的丝氨酸和跨膜结构域3中的甲硫氨酸对于大多数全身麻醉药的作用至关重要。我们研究了这些残基对于它们在苯二氮䓬敏感的GABA受体亚型α(2)β(3)γ(2)上的作用是否同样相关。我们发现，不仅N265M突变，而且M286W突变几乎消除了依托咪酯的调节作用。然而，依托咪酯的结构类似物抗惊厥药氯雷唑对N265M突变体无活性，但对M286W突变体显示出正常的调节活性。两种突变均不影响神经甾体阿法沙龙的调节作用。然而，阿法沙龙的直接作用在M286W突变体中显著增强，达到最大GABA电流的约两倍，但在N265M突变体中未受到显著影响。这些数据表明，各种全身麻醉药的调节作用和直接作用的结构要求是不同的。这些突变诱导的分子开关可用于确定全身麻醉药作用的分子决定因素。
