Figure 2.

Channel block and ionic permeability of the spontaneous current of homomeric ρ1(T314A) receptors expressed in Xenopus oocytes. (A) Typical current displayed in an oocyte injected with ρ1(T314A) cRNA. Application of 100 μM 3-aminopropy[methyl]phosphinic acid (3-APMPA) had no effect on this current. PTX (10–1,000 μM) blocked the spontaneous inward current in a dose-dependent manner, as indicated by the appearance of an apparently outward current. (B) Normalized PTX dose-inhibition curve for ρ1(T314A) receptors. Data points represent mean ± SD (n ≥ 4 oocytes). The line is the fit to the Hill equation, I = I_max/(1 + {[A]/IC₅₀}^n_H), where [A] is the PTX concentration and n_H is the Hill coefficient. The fit yielded an IC₅₀ and Hill coefficient of 14.2 μM and 0.9, respectively. (C) Typical current–voltage relationship of the spontaneous current recorded from an oocyte injected with ρ1(T314A) cRNA in the absence of ligand, in the presence of 0.1 μM GABA, and in the presence of 200 μM PTX in normal frog Ringer’s solution.