PLATELET SHAPE CHANGE AND CA2+ MOBILIZATION INDUCED BY COLLAGEN, BUT NOT THROMBIN OR ADP, ARE INHIBITED BY PHENYLARSINE OXIDE

In this report we have examined the effects of the protein tyrosine ph osphatase inhibitor phenylarsine oxide (PAO) on receptor-mediated plat elet shape change, secretion and aggregation. PAO was found to inhibit platelet aggregation induced by collagen, thrombin, ADP and epinephri ne at IC50 values of 0.35 mu mol/l, 2.5 mu mol/l, 0.2 mu mol/l and 0.3 mu mol/l, respectively. Agonist-induced secretion of ATP was inhibite d at similar or lower concentrations of PAO. The specificity of the in teraction of PAO with platelet proteins was demonstrated by the abilit y of the disulfhydryl compound 2,3-dimercaptopropanol, which abstracts PAO from proteins to form a stable cyclic adduct, to reverse PAO inhi bition of both agonist-induced platelet secretion and aggregation. Dim ercaptopropanesulphonic acid, a membrane-impermeable analogue of dimer captopropanol, did not reverse inhibition of collagen-induced shape ch ange or aggregation by PAO, thereby demonstrating that PAO acted intra cellularly. PAO inhibited collagen-induced shape change and internal C a2+ mobilization but had no effect on these two phenomena when induced by thrombin or ADP. PAO was also unable to prevent arachidonic acid-i nduced shape change, indicating that PAO acts at a site prior to the p hospholipase A(2)-mediated release of arachidonic acid to inhibit coll agen-induced shape change. PAO induced the accumulation of a number of phosphotyrosine-containing proteins and inhibited the collagen-induce d phosphorylation of a 40kD protein. The potency and agonist-specific effects of PAO on platelet activation suggest that this inhibitor will be of value in elucidation of signal transduction pathways involved i n receptor-mediated platelet function.