Fig. 5. Etomidate direct activation concentration responses. (A–D ) Four pairs of current traces, recorded from Xenopus  oocytes expressing different concatenated channels (labeled), are shown. Paired currents are each from a single oocyte, and were elicited with either maximal γ-aminobutyric acid (GABA) (1–3 mM) or maximal etomidate (0.3 mM). (E ) Concentration-response data (mean ± SD; n ≥ 4) for etomidate direct activation are shown for all four types of channels, normalized to maximal GABA responses: D^wtT^wt(half-solid squares ), D^αM236WT^αM236W(half-solid triangles ), D^αM236WT^wt(half-solid circles ), and D^wtT^αM236W(half-solid diamonds ). Lines  through data points are nonlinear least-squares fit to logistic functions (eq. 1, see Materials and Methods). The 1 mM etomidate data were excluded from the fit for D^αM236WT^αM236Wreceptors, because a second inhibitory effect of etomidate was evident. Fitted logistic parameters are reported in table 1.