SITES OF VOLATILE ANESTHETIC ACTION ON KAINATE (GLUTAMATE-RECEPTOR-6)RECEPTORS

Molecular mechanisms of anesthetic action on neurotransmitter receptor s are poorly understood. The major excitatory neurotransmitter in the central nervous system is glutamate, and recent studies found that vol atile anesthetics inhibit the function of the alpha-amino-3-hydroxyiso xazolepropionic acid subtype of glutamate receptors (e.g. glutamate re ceptor 3 (GluR3)), but enhance kainate (GluR6) receptor function, We u sed this dissimilar pharmacology to identify sites of anesthetic actio n on the kainate GluR6 receptor by constructing chimeric GluR3/GluR6 r eceptors, Results with chimeric receptors implicated a transmembrane r egion (TM4) of GluR6 in the action of halothane. Site directed mutagen esis subsequently showed that a specific amino acid, glycine 819 in TM 4, is important for enhancement of receptor function by halothane (0.2 -2 mM). Mutations of Gly-819 also markedly decreased the response to i soflurane (0.2-2 mM), enflurane (0.2-2 mM), and 1-chloro-1,2,2-trifluo rocyclobutane (0.2-2 mM). The nonanesthetics 1,2-dichlorohexafluorocyc lobutane and 2,3-dichlorooctafluorobutane had no effect on the functio ns of either wild-type GluR6 or receptors mutated at Gly-819. Ethanol and pentobarbital inhibited the function of both wild-type and mutant receptors. These results suggest that a specific amino acid, Gly-819, is critical for the action of volatile anesthetics, but not of ethanol or pentobarbital, on the GluR6 receptor.