Src kinase inhibitor PP1 potentiates the P2Y₁₂ component of the ADP-induced calcium response. Washed platelets previously loaded for 45 minutes with Fura 2-AM (3 μM) were incubated for 25 minutes with either PP1 (20 μM) or PP3 (20 μM) and/or 5 minutes with AR-C69931MX (1 μM) or A3P5P (200 μM), as indicated. (A) A time course of response representative of 3 separate experiments is shown. (B) The peak rise in intracellular calcium elicited by ADP (10 μM) was measured and plotted for each condition as indicated. Data shown are mean ± SEM (n > 3).