Model illustration of P2X2aR pore dilation with the kinetic model. (A) Current simulations are obtained by stimulating model cells with 100 µM ATP for 70 s under conditions specified by NMDG⁺ (black)- and Na⁺ (gray)-containing media. Because the holding potential is +60 mV, an outward current is generated in both cases. The decline in the current with NMDG⁺ case is steeper than with Na⁺ because E₁₂ is more negative in the former than in the latter. (B) Current simulation obtained during 100-µM ATP stimulation for 70 s and −80 to +80 voltage ramps delivered twice per second with parameters corresponding to NMDG⁺-containing medium. (C) I-V curves generated by the kinetic model during 70-s stimulation with 100 µM ATP and applying −80 to +80–mV voltage ramps twice per second in Na⁺-containing medium. There is little or no shift in reversal potential, but the slopes of the I-V curves decrease. (D) The time course of the current generated using the same conditions described in C. The amplitude of both inward and outward currents declines, resulting in a decrease in the slopes of the I-V curves shown in C.