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Inhibition of thrombin and SFLLR-peptide stimulation of platelet aggregation, phospholipase A2 and Na+/H+ exchange by a thrombin receptor antagonist

1995; Elsevier BV; Volume: 49; Issue: 4 Linguagem: Inglês

10.1016/0006-2952(94)00473-y

1873-2968

Steven M. Seiler, Marianne Peluso, Inge M. Michel, Harold Goldenberg, John W. Fenton, Douglas Riexinger, Sesha Natarajan,

Coagulation, Bradykinin, Polyphosphates, and Angioedema

A thrombin receptor has been described that is activated by thrombin cleavage generating a new N-terminus. The newly exposed SFLLR-containing "tethered-ligand" then activates the receptor. In these studies, we used 3-mercapto-propionyl-Phe-Cha-Cha-Arg-Lys-Pro-Asn-Asp-Lys-amide (Mpapeptide) as a thrombin receptor antagonist. This compound was capable of preventing both thrombin- and SFLLR-peptide-induced platelet aggregation with little effect on collagen-induced platelet aggregation. It also prevented thrombin- and SFLLRNP-induced calcium mobilization with little effect on thromboxane receptor-activated platelet Ca2+ mobilization. Platelet membrane GTPase could be activated by peptides that activated the thrombin receptor, and the thrombin receptor antagonist also prevented receptor-stimulated GTPase activity. Platelet phospholipase A2 (PLA2) activity (measured as the release of radiolabeled arachidonic acid) and Na+/H+ exchange activation were stimulated by α-thrombin and by SFLLR-containing peptides. Activation of both processes with low concentrations of thrombin required thrombin's anion-binding exosite, as they were not activated by similar concentrations of γ-thrombin, and the α- and ζ- thrombin activation was blocked by peptides mimicking the C-terminal region of hirudin. Stimulation of PLA2 and Na+/H+ exchange by both thrombin and SFLLR-containing peptides was inhibited by the thrombin receptor antagonist Mpa-peptide. These results support the hypothesis that thrombin stimulation of PLA2 activity and Na+/H+ exchange occurs via activation of the thrombin tethered-ligand receptor. Moreover, these data are consistent with the tethered-ligand receptor mediating most actions elicited by low concentrations of α-thrombin involved in human platelet activation.