FIGURE 4.

Antagonist action at P2X1 receptor mutants E52C to G96C. An EC₉₀ concentration of ATP was applied to oocytes expressing P2X1 WT and P2X1 receptor mutants E52C to G96C. Antagonists were applied to the P2X1 receptor using concentrations that inhibited the WT response by ∼50%, suramin (3 μm) and PPADS (1 μm). A, representative recordings of Y90C (i), a P2X1 mutant with increased suramin sensitivity, and I62C, a P2X1 mutant with increased PPADS sensitivity (ii). Traces show the response in the presence of ATP only (open circle) and in the presence of ATP and the antagonist (closed circle). ATP was applied for 3 s (black bar), and the antagonists were bath-perfused 5 min before recording. B, Schild plot analysis of suramin antagonism at the WT P2X1 receptor and the mutant Y90C. C, percentage inhibition of EC₉₀ concentration of ATP in the presence of the antagonists suramin (3 μm) (i) and PPADS (1 μm) (ii) on P2X1 receptor mutants E52C to G96C (n = 3–4). *, p < 0.05; **, p < 0.01. Error bars, S.E. Conserved residues are highlighted in black.