FIGURE 5.

Removal of lysine residues from the human can reduce sensitivity to NF449. A, representative traces of membrane currents evoked by ATP (10 μm), applied for 1 s as indicated by the horizontal bar. Left panels, control. Center and right panels, in NF449 (3 and 300 nm). B, ATP concentration-response curves for wild type human P2X₁ receptors and for receptors with one or four lysines removed at the positions indicated. Open symbols, control. Solid symbols, in presence of NF449 (3 and 300 nm). Note the decreased effectiveness of NF449 (300 nm) as an antagonist in the case of human P2X₁[K138E] and also for human P2X₁[No K] receptors.