The actions of ether, alcohol and alkane general anaesthetics on GABAA and glycine receptors and the effects of TM2 and TM3 mutations

摘要

The actions of 13 general anaesthetics (diethyl ether, enflurane, isoflurane, methoxyflurane, sevoflurane, chloral hydrate, trifluoroethanol, tribromoethanol, tert-butanol, chloretone, brometone, trichloroethylene, and α-chloralose) were studied on agonist-activated Cl− currents at human GABAA α2β1, glycine α1, and GABAC ρ1 receptors expressed in human embryonic kidney 293 cells.All 13 anaesthetics enhanced responses to submaximal (EC20) concentrations of agonist at GABAA and glycine receptors, except α-chloralose, which did not enhance responses at the glycine α1 receptor. None of the anaesthetics studied potentiated GABA responses at the GABAC ρ1 receptor.Potentiation of submaximal agonist currents by the anaesthetics was studied at GABAA and glycine receptors harbouring mutations in putative transmembrane domains 2 and 3 within GABAA α2, β1, or glycine α1 receptor subunits: GABAA α2(S270I)β1, α2(A291W)β1, α2β1(S265I), and α2β1(M286W); glycine α1(S267I) and α1(A288W). For all anaesthetics studied except α-chloralose, at least one of the mutations above abolished drug potentiation of agonist responses at GABAA and glycine receptors.α-Chloralose produced efficacious direct activation of the GABAA α2β1 receptor (a ‘GABA-mimetic' effect). The other 12 anaesthetics produced minimal or no direct activation of GABAA and glycine receptors. A non-anaesthetic isomer of α-chloralose, β-chloralose, was inactive at GABAA and glycine receptors and did not antagonize the actions of α-chloralose at GABAA receptors.The implications of these findings for the molecular mechanisms of action of general anaesthetics at GABAA and glycine receptors are discussed.