Src does not regulate P2Y₁₂-mediated inhibition of cAMP but negatively feeds back on the PI3K component of the P2Y₁₂-mediated contribution to the calcium response. Washed platelets were incubated with forskolin (10 μM) and IBMX (10 μM) for 60 minutes. Platelets were then incubated for 1 minute with EGTA (1 mM) and stimulated for 3 minutes with ADP (10 μM), where indicated. Some platelets were incubated prior to stimulation with either PP1 (20 μM) or PP3 (20 μM) for 25 minutes and/or A3P5P (1 mM) or AR-C69931MX (1 μM) for 5 minutes, as indicated. Reactions were stopped by addition of one-tenth volume 100% TCA and cAMP assayed as described in “Materials and methods.” The cAMP accumulation is expressed as a percentage of the accumulation for samples treated with forskolin/IBMX alone (mean ± SEM; n = 3).