Fig. 1.

Chimeric hP2X7-1 receptors identify regions important for action of the P2X7R-selective antagonists A438079 and A740003. (A) Sequence alignment of the extracellular loop of the human P2X1 and P2X7Rs. Residues in black are conserved between human P2XR paralogs, gray residues are variant between human P2XR paralogs, and red residues are unique to the P2X7R. Colored boxes show the regions of P2X7 that were replaced with the corresponding residues from the P2X1R to generate the chimeras. (B) Effects of the antagonist A438079 (3 μM, traces indicated by black circles) on currents evoked by an EC₉₀ concentration of ATP (3s application indicated by black bar) at the P2X7-2Nβ, 279–285 chimera and P2X1R. Control responses are indicated by open circles. (C) Concentration-dependent inhibition by A438079 of responses to an EC₉₀ concentration of ATP for P2X7-2Nβ (gray), 73–79 del (red), chimeras 295–310 (orange), 279–285 (light green), and P2X1 (black). (D) Histogram showing the pIC₅₀ of A438079 at P2X7-2Nβ and chimeric receptors. (E) Location of chimeras that reduced A438079 action mapped on a pdP2X7R-based homology model. Chimeras with no change are shown as gray spheres. (F) Effects of the antagonist A740003 (0.3 μM, traces indicated by black circles) on currents evoked by an EC₉₀ concentration of ATP (3s application indicated by black bar) at the P2X7-2Nβ, 295–310 chimera and P2X1R. Control responses are indicated by open circles. (G) Concentration-dependent inhibition by A740003 of responses to an EC₉₀ concentration of ATP for P2X7-2Nβ (gray), chimeras 112–118 (light blue), 295–310 (orange) and 89–94 (green), and P2X1 (black). (H) Histogram showing the pIC₅₀ of A740003 at P2X7-2Nβ and chimeric receptors. (I) Location of chimeras with an effect on A740003 action mapped on a pdP2X7R-based homology model. Chimeras with no change are shown as gray spheres. n ≥ 3, exact values given for each receptor tested are shown in Table 1. *P < 0.05; **P < 0.01; ****P < 0.0001.