Figure 3.

Responses of M2 domain mutant ρ1(T314A) and WT receptors to GABA. (A) Typical responses of mutant ρ1(T314A) homomeric receptors to GABA. Two traces are illustrated from two different oocytes. GABA concentrations >0.1 μM produced an additional transient inward current, indicated by arrows. (B) Normalized GABA dose-response relationship for ρ1(T314A) receptors. Measurements were made after the effect of GABA had reached a plateau (steady state). Data points represent mean ± SD (n ≥ 5 oocytes). For [GABA] ≤ 0.1 μM, the dotted line is the fit to the Hill equation. The fit yielded an IC₅₀ and Hill coefficient of 0.11 μM and 0.8, respectively. (C) Typical responses of WT ρ1 receptors to GABA. GABA (≤0.1 μM) did not evoke any detectable current. (D) Inhibitory effects of GABA (0.1 and 1 μM) on the spontaneous current of the ρ1(T314A) receptor were blocked by 100 μM 3-APMPA. (E) Demonstration that suppression of current produced by 0.1 μM GABA is not due to receptor desensitization. Three GABA responses on ρ1(T314A) receptors were recorded from different oocytes. Traces in A, D, and E are normalized to the amplitude of the initial spontaneous current, and thus the ordinate values represent arbitrary units.