Concentration-dependent effects of ATP on activation and desensitization of inward current in HEK293 cells expressing P2X2aR and P2X2bR whole cell recording. (A) Typical pattern of P2X2aR (left) and P2X2bR (right) currents in response to variable ATP concentrations. Traces shown are obtained during the third application of ATP. Gray lines, experimental traces; black lines, fitted curves. τ is from monoexponential fitting. (B) Dependence of the peak current amplitude on agonist concentration in cells expressing P2X2aR (left) and P2X2bR (right). (C) Dependence of the level of receptor desensitization on agonist concentration in cells expressing P2X2aR (left) and P2X2bR (right). In A, representative traces are shown; in B and C, mean ± SEM values from at least four recordings per dose are shown.