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

1 The actions of 13 general anaesthetics (diethyl ether, enflurane, isoflur ane, methoxyflurane, sevoflurane, chloral hydrate, trifluoroethanol, tribro moethanol, tert-butanol, chloretone, brometone, trichloroethylene, and alph a-chloralose) were studied on agonist-activated Cl- currents at human GABA( A) alpha(2)beta(1), glycine alpha(1), and GABA(c) rho(1) receptors expresse d in human embryonic kidney 293 cells. 2 All 13 anaesthetics enhanced responses to submaximal (EC20) concentration s of agonist at GABA(A) and glycine receptors, except alpha-chloralose, whi ch did not enhance responses at the glycine alpha(1) receptor. None of the anaesthetics studied potentiated GABA responses at the GABA(c) rho(1) recep tor. 3 Potentiation of submaximal agonist currents by the anaesthetics was studi ed at GGBA(A) and glycine receptors harbouring mutations in putative transm embrane domains 2 and 3 within GABAA alpha(2), beta(1), or glycine alpha(1) receptor subunits: GABA(A) alpha(2)(S270I)beta(1), alpha(2)(A291W)beta(1), alpha(2)beta(1)(S265I), and alpha(2)beta(1)(M286W); glycine alpha(1)(S267I ) and alpha(1)(A288W). For all anaesthetics studied except alpha-chloralose , at least one of the mutations above abolished drug potentiation of agonis t responses at GABA(A) and glycine receptors. 4 alpha-Chloralose produced efficacious direct activation of the GABA(A) al pha(2)beta(1) 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 alpha-chloralose, beta-chloralose, was inactiv e at GABA(A) and glycine receptors and did not antagonize the actions of al pha-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.