Competitive inhibition by A3P5P of ADP-induced [Ca²⁺]_i increases in washed human platelets (A) and in Jurkat cells stably expressing the human P2Y₁receptor (B). [Ca²⁺]_i was stimulated by ADP alone or in the presence of increasing concentrations of A3P5P, in the presence of 2 μmol/L external calcium. (C) Effects of increasing concentrations of A2P5P and A3P5P on [Ca²⁺]_i increases induced by 1 μmol/L ADP in B10 cells. (D) A3P5P (100 μmol/L) (2) did not inhibit [Ca²⁺]_i increases induced by 2 μmol/L U46619 (1, left] or 0.1 U/mL thrombin (1, right) in washed human platelets. Curves each represent the mean of three independent experiments and bars show the SEM.