Fig. 3

Figure 3. Altered apparent ATP affinities of ATP in P2X mutants. A–I, concentration–response curves of ATP in WT and equivalent alanine substitutions in zfP2X4 (A), rP2X4 (B), hP2X3 (C), AmP2X (D), ckP2X7 (E), pdP2X7 (F), hP2X7 (G), hP2X1 (H), and hP2X2 (I). The solid lines are fitted by Hill equation (mean ± SD, n = 3–7, EC₅₀ = 1426 ± 733 and 89.6 ± 18.1 μM, n_H = 0.94 ± 0.16 and 1.02 ± 0.18 for zfP2X4^WT and zfP2X4^E121A; EC₅₀ = 7.65 ± 1.56 and 45.92 ± 9.05 μM, n_H = 1.20 ± 0.22 and 1.11 ± 0.15 for rP2X4^WT and rP2X4^E118A; EC₅₀ = 0.45 ± 0.07 and 0.58 ± 0.07 μM, n_H = 0.94 ± 0.16 and 1.02 ± 0.18 for hP2X3^WT and hP2X3^E109A; EC₅₀ = 43.5 ± 4.7 and 32.9 ± 4.2 μM, n_H = 1.14 ± 0.11 and 0.99 ± 0.09 for AmP2X^WT and AmP2X^E129A; EC₅₀ = 4.77 ± 0.69 and 5.31 ± 1.26 μM, n_H = 1.14 ± 0.16 and 0.91 ± 0.16 for ckP2X7^WT and ckP2X7^E109A; EC₅₀ = 95.7 ± 17.6 and 96.6 ± 10.9 μM, n_H = 1.44 ± 0.32 and 1.53 ± 0.24 for pdP2X7^WT and pdP2X7^D121A; EC₅₀ = 496.7 ± 44.2 and 360.5 ± 54.3 μM, n_H = 1.71 ± 0.19 and 1.34 ± 0.20 for hP2X7^WT and hP2X7^E121A; EC₅₀ = 0.86 ± 0.16 and 0.92 ± 0.17 μM, n_H = 1.04 ± 0.16 and 1.46 ± 0.33 for hP2X1^WT and hP2X1^E119A; EC₅₀ = 13.16 ± 1.97 and 12.92 ± 1.68 μM, n_H = 1.15 ± 0.17 and 1.26 ± 0.15 for hP2X2^WT and hP2X2^E127A, respectively). I_max was defined as the saturating ATP-induced current for WT and equivalent alanine-substituted P2X receptors, except for the maximum concentration of ATP (3 mM) used for zfP2X4^E121A. J and K, representative current traces (J) and pooled data (K) for WT and equivalent alanine substitution of P2X receptors. The scatter of each open circle represents each measurement, n = 7, 4, 5, 5, 3, 4, 4, 5, 6, 5, 5, 5, 5, 5, 5, 6, 8, and 8, from left to right, respectively. AmP2X, gulf coast tick (Amblyomma maculatum) P2X; ckP2X7, chicken (Gallus gallus domesticus) P2X7; hP2X3, human (Homo sapiens) P2X3; pdP2X7, giant panda (Ailuropoda melanoleuca) P2X7; rP2X4, rat (Rattus norvegicus) P2X4; zfP2X4, zebrafish (Danio rerio) P2X4.