Figure 4.

Suramin activity at rP2X₄ receptor. (A) Histograms of ATP activity in the absence and presence of suramin (50 μM), and 20 min after washout of suramin. The agonist was applied at the respective EC₅₀ value at pH 7.5, 6.5 and 5.5, and control responses were taken as 1 (activity index=1). (B) Histograms of ATP activity in the absence and presence of Zn²⁺ ions, further addition of suramin (50 μM), and 20 min after washout of suramin and Zn²⁺ ions. Zn²⁺ was applied at 10 μM (pH 7.5 and 5.5) and 100 μM (pH 6.5), these concentrations causing maximal potentiation of ATP-responses at the above pH levels.