Addition of a submaximal concentration (200 μM) of A3P5P reveals a calcium response dependent upon P2Y₁₂ activation. Fura 2-loaded platelets were preincubated with various concentrations of A3P5P with or without addition of AR-C69931MX (1 μM). Platelets were then stimulated with ADP (10 μM) and the peak rise in cytosolic calcium concentration was measured and plotted against log concentration of A3P5P as shown. Box indicates that ARC completely ablates in the presence of 200 μM A3P5P. Data shown are mean ± SEM (n = 3).