Synergistic Effect of Thrombin on Collagen-Induced Platelet Procoagulant Activity Is Mediated Through Protease-Activated Receptor-1

• Published in: Arteriosclerosis, thrombosis, and vascular biology Vol. 25; no. 7; pp. 1499 - 1505
• Main Authors: Keuren, Jeffrey F.W, Wielders, Simone J.H, Ulrichts, Hans, Hackeng, Tilman, Heemskerk, Johan W.M, Deckmyn, Hans, Bevers, Edouard M, Lindhout, Theo
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Heart Association, Inc 01.07.2005; Hagerstown, MD Lippincott
• Subjects: Apoptosis Regulatory Proteins - metabolism; Atherosclerosis (general aspects, experimental research); Biological and medical sciences; Blood and lymphatic vessels; Blood coagulation. Blood cells; Blood Platelets - drug effects; Blood Platelets - metabolism; Calcium - pharmacokinetics; Cardiology. Vascular system; Collagen - metabolism; Collagen - pharmacology; Diseases of the peripheral vessels. Diseases of the vena cava. Miscellaneous; Drug Synergism; Fundamental and applied biological sciences. Psychology; General aspects; Hemostatics - metabolism; Hemostatics - pharmacology; Humans; In Vitro Techniques; Medical sciences; Molecular and cellular biology; Platelet; Platelet Glycoprotein GPIb-IX Complex - metabolism; Platelet Membrane Glycoproteins - metabolism; Receptor, PAR-1 - metabolism; Thrombin - metabolism; Thrombin - pharmacology; Thromboplastin - metabolism; Thrombosis - metabolism; Vertebrates: cardiovascular system; protease-activated receptors; Serine endopeptidases; Hemostatic; Enzyme; Glycoprotein; Cardiovascular disease; Thrombin; procoagulant activity; platelets; Vascular disease; Peptidases; Platelet; Collagen; Atherosclerosis; Hydrolases
• ISSN: 1079-5642; 1524-4636
• DOI: 10.1161/01.ATV.0000167526.31611.f6

OBJECTIVE—In the blood coagulation process, the rate of thrombin formation is critically dependent on phosphatidylserine (PtdSer) at the surface of activated platelets. Thrombin synergistically enhances the collagen-induced platelet procoagulant response. The objective of this study is to elucidate the mechanism of this synergistic action with a focus on the intracellular Ca concentration ([Ca]i) and the various platelet receptors for thrombin. METHODS AND RESULTS—We demonstrate that procoagulant activity is related to a sustained increased [Ca]i, which in turn depends on extracellular Ca influx. Increased PtdSer exposure coincides with increased [Ca]i and was observed in a subpopulation (≈14%) of the platelets after stimulation with thrombin plus collagen. 2D2-Fab fragments against the thrombin binding site on GPIbα made clear that this receptor did not signal for platelet procoagulant activity. Inhibition of protease-activated receptor 1 (PAR-1) and PAR-4 by selective intracellular inhibitors and selective desensitization of these receptors revealed that PAR-1, but not PAR-4, activation is a prerequisite for both sustained elevations in [Ca]i and procoagulant activity induced by collagen plus thrombin. CONCLUSIONS—The interaction of thrombin with PAR-1 mediates a synergistic effect on collagen-induced procoagulant activity by inducing a sustained elevation in [Ca]i in a subpopulation of platelets.