Distinct structural requirements for the direct and indirect actions of the anaesthetic etomidate at GABA(A) receptors

1. The intravenous anaesthetic etomidate augments GABA-gated chloride curre nts (indirect action) and, at higher concentrations, evokes chloride curren ts in the absence of GABA (direct action). 2. In order to identify amino ac id residues essential for these actions, site directed mutagenesis was perf ormed on the beta 3 subunit. 3. Mutation of an asparagine to a serine resid ue at position 290 dramatically reduced both etomidate-induced chloride cur rents 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 con trast, the indirect effect of etomidate was retained, though its potency wa s reduced. 5. These findings indicate that there are distinct requirements for these dual actions of etomidate at GABA(A) receptors. (C) 1998 Publishe d by Elsevier Science Ireland Ltd. All rights reserved.