Efficient tyrosine phosphorylation of proteins after activation of platelets with thrombin depends on intact glycoprotein Ib.

The role of platelet glycoprotein Ib as a thrombin receptor has been often a subject of controversy. We have investigated the role of the thrombin receptors, GPIb and protease-activated receptor (PAR)-1. Tyrosine phosphorylation in whole platelet lysates and in cytoskeletal extracts was evaluated after activation with thrombin and with the thrombin receptor-activating peptide (TRAP).

Platelet adhesion onto a polystyrene surface under static conditions: role of specific platelet receptors and effect of divalent cations.

An experimental model was used to elucidate the basic mechanisms involved in the interaction of platelets with an artificial surface. The role of divalent cations and the involvement of specific platelet membrane receptors were evaluated. Isolated platelets were allowed to interact with a polystyrene surface for 20 min in the presence of divalent cations (Ca2+, Mg2+ or Zn2+), a chelating agent (ethylenediaminetetraacetic, EDTA), and specific antibodies to the main platelet receptors, glycoproteins (GP) Ib and IIb-IIIa.

Inhibition of cytoskeletal assembly by cytochalasin B prevents signaling through tyrosine phosphorylation and secretion triggered by collagen but not by thrombin.

Activation of platelets leads to cytoskeletal assembly that is responsible for platelet motility and internal contraction. We have evaluated the involvement of the cytoskeleton in platelet activation by two strong agonists, collagen and thrombin. Activation was assessed by measuring changes in cytoskeletal assembly, externalization of activation-dependent markers and expression of procoagulant activity, and tyrosine phosphorylation of proteins, in both the absence and the presence of cytochalasin B.