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

Biochem Pharmacol. 1995 Feb 14;49(4):519-28. doi: 10.1016/0006-2952(94)00473-y.


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 alpha-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 gamma-thrombin, and the alpha- and zeta-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 alpha-thrombin involved in human platelet activation.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenylyl Cyclase Inhibitors
  • Amino Acid Sequence
  • Blood Platelets / metabolism
  • Humans
  • Molecular Sequence Data
  • Oligopeptides / antagonists & inhibitors*
  • Oligopeptides / pharmacology
  • Phospholipases A / antagonists & inhibitors*
  • Phospholipases A2
  • Platelet Activation / drug effects*
  • Platelet Aggregation / drug effects*
  • Platelet Aggregation Inhibitors / pharmacology
  • Receptors, Thrombin / antagonists & inhibitors*
  • Sodium-Hydrogen Exchangers / antagonists & inhibitors*
  • Thrombin / antagonists & inhibitors*


  • Adenylyl Cyclase Inhibitors
  • C186 65
  • Oligopeptides
  • Platelet Aggregation Inhibitors
  • Receptors, Thrombin
  • Sodium-Hydrogen Exchangers
  • Phospholipases A
  • Phospholipases A2
  • Thrombin