Functional characterization of α1β3H267Cγ2L γ-aminobutyric acid (GABA) type A receptors. (A) Traces are currents measured from a single voltage-clamped oocyte expressing α1β3H267Cγ2L GABA type A receptors. Bars over the traces identify GABA concentration (μM) and period of exposure. (B) Traces are recorded from the same oocyte as in A, activated with various GABA concentrations combined with 5 μM propofol (PRO). (C) Combined GABA concentration–responses from three oocytes in the absence and presence of propofol. Normalized data were fitted with equation 1 (see Materials and Methods). Fitted GABA EC₅₀ values are 25 μM with GABA alone and 1.6 μM in the presence of 5 μM propofol. (D) Picrotoxin (PTX) application to a voltage-clamped oocyte expressing α1β3H267Cγ2L receptors reveals an absence of spontaneous gating activity. Combining propofol (10 μM) with maximal (1 mM) GABA does not enhance peak current, indicating that GABA alone activates approximately 100% of receptors.