Distinct structural requirements for the direct and indirect actions of the anaesthetic etomidate at GABAA receptors

1. The intravenous anaesthetic etomidate augments GABA-gated chloride currents (indirect action) and, at higher concentrations, evokes chloride currents in the absence of GABA (direct action). 2. In order to identify amino acid residues essential for these actions, site directed mutagenesis was performed on the beta 3 subunit. 3. Mutation of an asparagine to a serine residue at position 290 dramatically reduced both etomidate-induced chloride currents and its ability to enhance [H-3]flunitrazepam binding in HEK293 cells expressing alpha 1 beta 3 gamma 2 recombinant GABA(A) receptors. 4. In contrast, the indirect effect of etomidate was retained, though its potency was reduced. 5. These findings indicate that there are distinct requirements for these dual actions of etomidate at GABA(A) receptors. (C) 1998 Published by Elsevier Science Ireland Ltd. All rights reserved.