thromboxane-a2 and arginyl-glycyl-aspartyl-serine

Washed platelets from either normal donors or patients with thrombasthenia lacking in integrin GPIIb-IIIa were stimulated by thrombin or STA2 with stirring and their kinetics of protein-tyrosine phosphorylation were compared. The early increase in protein-tyrosine phosphorylation on 115 and 75 kDa protein bands was observed within 10 s after stimulation in both normal and thrombasthenic platelets. While both 115 and 75 kDa tyrosine-phosphorylated protein bands were quickly dephosphorylated in normal platelets, thrombin-induced 115 kDa or STA2-induced 115 and 75 kDa protein bands were not dephosphorylated in thrombasthenic platelets. The delay of phosphotyrosine-specific dephosphorylation on those protein bands was observed when thrombin- or STA2-induced aggregation of normal platelets was inhibited by RGDS, an inhibitor of fibrinogen binding to GPIIb-IIIa. These data indicate that fibrinogen binding to GPIIb-IIIa is involved in the regulation of phosphotyrosine-specific dephosphorylation on certain protein bands.

Topics: Amino Acid Sequence; Antibodies; Antibodies, Monoclonal; Blood Platelets; Humans; Immunoblotting; In Vitro Techniques; Kinetics; Molecular Weight; Oligopeptides; Phosphoproteins; Phosphotyrosine; Platelet Membrane Glycoproteins; Reference Values; Thrombasthenia; Thrombin; Thromboxane A2; Tyrosine

Aggregation of platelets, stimulated by different agonists, was inhibited by omitting sample stirring or by preincubation of platelets with a monoclonal antibody against glycoproteins IIb-IIIa or with a pentapeptide containing the sequence Arg-Gly-Asp-Ser. In platelets stimulated by collagen, ADP and epinephrine, the inhibition of aggregation paralleled a reduction of both release reaction and thromboxane A2 formation. When thrombin was the stimulus, ATP release and thromboxane A2 production were unaffected (or only slightly modified) by the inhibition of platelet aggregation. These data add further evidence to the hypothesis that aggregation supports the activation of platelets stimulated by weak agonists.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Antibodies, Monoclonal; Blood Platelets; Collagen; Epinephrine; Humans; Oligopeptides; Platelet Aggregation; Platelet Aggregation Inhibitors; Platelet Membrane Glycoproteins; Thromboxane A2; Thromboxane B2