Agonist-mediated phosphorylation of Y311 residue of PKCδ in platelets. Washed and aspirin-treated platelets were stimulated with either SFLLRN or AYPGKF (A), 10 μM ADP (adenosine diphosphate) for different time periods (B), or with PAR agonists in the presence or absence of ADP receptor antagonists (C) at 37°C, and the reaction was stopped by adding the Laemmlli buffer. Stimulation with SFLLRN was for 20 seconds and AYPGKF was for 1 minute. The lysates were analyzed by Western blotting by using an antibody directed against the phosphorylated Y311 residue of PKCδ. Equal lane loading was assured by probing the samples with PKCδ antibody. The Western blot shown is representative of experiments done using platelets from 3 different donors. AYP indicates AYPGKF, 500 μM.