Shear stress alone can activate platelets resulting in a subsequent platelet aggregation, so-called 'shear-induced platelet aggregation'. In our work, we analyzed how differently elevated shear stress impacts the Src and focal adhesion kinase (FAK) activation in fibrinogen-adherent human platelets. We detected the extents of Src pY418 and FAK pY397 activations in platelets on immobilized fibrinogen and over BSA under shear conditions. Moreover, we analyzed the role of [alpha]IIb[beta]3 in the shear-induced platelet signaling by performing our experiments in the presence of the [alpha]IIb[beta]3-antagonist Abciximab. Abnormally high shear rates (5000 s-1) significantly increased the extent of phosphorylation of both tyrosine kinases after short (2 min) incubation time independently of the presence or absence of the integrin [alpha]IIb[beta]3 ligand, fibrinogen. We could see considerably greater Src activation on immobilized fibrinogen than on BSA, but the extent of FAK Y397 phosphorylation was independent on the matrix. Abciximab not only reduced the Src and FAK signaling in platelets exposed to 5000 s-1 on immobilized fibrinogen, but in platelets exposed to 5000 s-1 over BSA as well. Our data indicate that whereas Src activation under shear stress is dominantly ligand-dependent, FAK signaling seems to be mostly shear induced.
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