FIGURE 1.

Effect of point cysteine mutations on ATP potency. Agonist action was tested on P2X1 WT and P2X1 receptor mutants expressed in oocytes by two-electrode voltage clamp (holding potential, −60 mV). A, concentration responses to ATP for oocytes expressing WT, K68C, K70C, and F92C mutant P2X1 receptors. ATP was applied for 3 s (indicated by the black bar; scale bar, 1 μA for all). B, summary of concentration response data for WT and mutants K68C, K70C, and F92C, which showed a significant decrease in ATP potency (n = 3–4). Error bars, S.E. The inset represents the slower response times of K68C, K70C, and F92C compared with WT in response to a maximum concentration of ATP. C, autoradiograph depicting radiolabeled [³²P]2-azido-ATP cross-linked to WT and mutant receptors (mean EC₅₀ for ATP (in μm) is shown in parentheses). D, summary showing pEC₅₀ values of all mutants compared with WT (left). Values are shown as means ± S.E. Significant differences from the wild type are indicated (***, p < 0.001). Conserved residues are highlighted in black.