FIGURE 1.

PKC inhibition reduces platelet aggregation and secretion as well as selectively modulates Syk tyrosine phosphorylation on Tyr-525/526. A, human platelets were incubated with 5 μm GFX for 5 min prior to stimulation with the GPVI agonist Cvx (200, 400, or 800 ng/ml). Platelet aggregation and secretion were measured for 2 min. Bi, platelets were treated as described in A, stimulated with 200 ng/ml Cvx for 0, 30, 60, and 180 s, and phosphotyrosine 525/526 Syk and total Syk were analyzed. Bii, quantitation of the blots with mean ± S.E. (error bars) of relative Syk phosphorylation for Cvx in untreated (●) and GFX treated (▴) platelets was plotted against time, and Student's t test was performed (p < 0.05, untreated versus GFX treated platelets). C and D, results are the same as B except that platelets were stimulated using GPVI agonist 10 μg/ml collagen (C) and 5 μg/ml collagen-related peptide (CRP) (D). E, washed murine platelets were treated same as in Bi but stimulated with 1 μg/ml Cvx and probed for pSyk Tyr-525/526 and total Syk. Blots are representative of at least three independent experiments.