The actions of ether, alcohol and alkane general anaesthetics on GABA(A) and glycine receptors and the effects of TM2 and TM3 mutations

Abstract

1. 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 GABA(A) α2β1, glycine α1, and GABA(C) ρ1 receptors expressed in human embryonic kidney 293 cells. 2. All 13 anaesthetics enhanced responses to submaximal (EC20) concentrations of agonist at GABA(A) 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 GABA(C) ρ1 receptor. 3. Potentiation of submaximal agonist currents by the anaesthetics was studied at GABA(A) and glycine receptors harbouring mutations in putative transmembrane domains 2 and 3 within GABA(A) α2, β1, or glycine α1 receptor subunits: GABA(A) 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 GABA(A) and glycine receptors. 4. α-Chloralose produced efficacious direct activation of the GABA(A) α2β1 receptor (a 'GABA-mimetic' effect). The other 12 anaesthetics produced minimal or no direct activation of GABA(A) and glycine receptors. A non-anaesthetic isomer of α-chloralose, β-chloralose, was inactive at GABA(A) and glycine receptors and did not antagonize the actions of α-chloralose at GABA(A) receptors. 5. The implications of these findings for the molecular mechanisms of action of general anaesthetics at GABA(A) and glycine receptors are discussed.