Voltage-dependent activation of P2X₂ during the steady state after application of ATP. Macroscopic currents recorded under two-electrode voltage clamp using Xenopus oocytes in Na-based external solution during the steady state after application of ATP. (A) Current traces from an identical oocyte evoked by a hyperpolarizing step pulse (from −40 to −100 mV) in the absence (dashed line) and presence (solid line) of ATP. The actual membrane potentials recorded are indicated in the bottom panel. The instantaneous component (a), activation component (b), and deactivation component (c) are illustrated. (B) Comparison of macroscopic currents evoked by hyperpolarizing step pulses from two different prepulse potentials, +60 and −60 mV. Pulse protocols are indicated below. These current traces were recorded from an identical oocyte and shown after subtracting data obtained in the absence of ATP. (C) Current traces from an identical oocyte evoked by hyperpolarizing step pulses to −120 from −30-mV prepulses of different durations. The pulse protocols are indicated below. Current traces were overlaid by arranging them relative to the beginning of the prepulse. (D) Comparison of macroscopic currents evoked by hyperpolarizing step pulses during the steady state after the application of various [ATP]. The pulse protocols are indicated on the right. These current traces were recorded from an identical oocyte and shown after subtracting data obtained in the absence of ATP. (E) I_activation/I_steady ratio from an identical oocyte after different prepulse potentials and [ATP]. Data points obtained at the same [ATP] are connected by lines.