Analyses of the voltage-dependent gating of P2X₂ in the presence of various [ATP]. (A) Dependence of the activation kinetics on voltage and [ATP]. The activation phases of the currents shown in Fig. 2 were fitted with a single exponential function, and the time constants of the fittings at each membrane potential are plotted. (B) [ATP] response relationships are derived from the recordings in Fig. 2. Current amplitudes were measured at the test pulse. Data were fitted with Hill's equation as described in Materials and methods. (C) [ATP] response relationships in B were normalized and replotted. (D) Voltage dependency of EC₅₀ values of the [ATP] response. Representative plots (filled circles) are derived from the data in B and C; the others (open circles) are from other oocytes. (E) Normalized G-V relationships are derived from the recording in Fig. 2. Tail current amplitudes at −60 mV were measured. Data were fitted with the two-state Boltzmann equation as described Materials and methods. (F and G) V_1/2 values (F) and Z values (G) in various [ATP]. Representative plots (filled circles) were derived from the data in E; the others (open circles) are from other oocytes.