Characterization of P2X2aR pore dilation. All recordings were done in HEK293 cells. (A and B) Patterns of 100 µM ATP-induced current in cells bathed in medium containing 155 mM NMDG⁺, 10 mM HEPES, and 10 mM glucose. (A) Currents displayed during initial 40-s agonist application at +60 mV. (B) Time course of agonist-induced current under the ramp protocol. (C) Positive shifts in reversal potential observed during the initial 9-s application of 100 µM ATP to a cell bathed in medium containing 140 mM NMDG⁺, 15 mM NaCl, 10 mM HEPES, and 10 mM glucose. (D–F) Patterns of 100 µM ATP-induced responses when Na⁺ concentration was identical in the extracellular and intracellular solutions (145 mM). Bath medium also contained 10 mM HEPES and 10 mM glucose. (D) Representative whole cell recording at a holding potential of +60 mV. (E) Time course of agonist-induced current under the ramp protocol. (F) There is no positive shift in reversal potential but a gradual decrease in the slope of current during 45-s agonist application. Shown are 10 ramps spaced by 5 s. (G–I) Patterns of 100 µM ATP-induced responses in cells bathed in KR buffer. (G) Representative whole cell recording at a holding potential of +60 mV. (H) Time course of agonist-induced current under the ramp protocol. (I) The progressive decrease in the slope of current during 45-s agonist application. Shown are 10 ramps spaced by 5 s. In all cases, 485-ms voltage ramps were delivered twice per 1 s from a holding potential of 0 mV (C) and −60 mV (F and I).