The site of action of general anesthesia is unknown but remains an important clinical issue. Converging lines of evidence have recently implicated the GABAA receptor complex (GRC) as having a role in mechanism of unconsciousness. The primary goal of this project is to elucidate the actions of general anesthetics at this receptor complex and to test the hypothesis that general anesthetics exert some of their effects via modulation of the GABAA receptor. We will examine the effects of the stereoisomers of volatile anesthetics on the characteristics of ligands that bind to the GRC. Specifically, inhalation agents have been shown to potentiate the binding of both benzodiazepines and the GABA-mimetic muscimol. The presence of stereoselective effects of halothane on these sites will provide strong evidence that they represent specific interactions with halothane. Moreover, these data will support the hypothesis that stereoselective effects at the GRC are not unique to isoflurane but are shared by other volatile anesthetics. We will also study the effects of these agents and their stereoisomers on transformed cells which contain GRC's of known subunit composition. The use of stereoisomers will greatly enhance the detection of the subunits needed for anesthetic effects. Moreover, stereoisomers exist for anesthetic secondary alcohols. We will use these optical isomers to determine if their stereochemistry confers differential effects upon the ability of the optical isomers to alter binding at the GRC. This will provide information as to whether the stereospecificity is a characteristic generalizable to many anesthetics or is found only in the volatile class. In addition, we will investigate the actions the general anesthetic isomers on several receptor systems other than the GRC (such as L-type calcium channels) to determine if stereospecificity is a feature unique to the GRC. This will provide information about the anesthetic actions on other systems where side effects may be mediated as well as place the findings in perspective. An increased understanding of the site of anesthetic action will be valuable both by increasing our understanding of consciousness and in the rational design of drugs with fewer side effects.
