Thromb Haemost 2003; 90(02): 299-316
DOI: 10.1160/TH03-02-0103
Platelets and Blood Cells
Schattauer GmbH

The role of PAR4 in thrombin-induced thromboxane production in human platelets

Chin-Chung Wu
1   Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung,
,
Tsong-Long Hwang
2   Graduate Institute of Natural Products, College of Medicine, Chang Gung University, Taoyuan
,
Chang-Hui Liao
2   Graduate Institute of Natural Products, College of Medicine, Chang Gung University, Taoyuan
,
Sheng-Chu Kuo
3   Graduate Institute of Pharmaceutical Chemistry, China Medical College, Taichung,
,
Fang-Yu Lee
4   Yung-Shin Pharmaceutical Industry Co. Ltd, Taichung
,
Che-Ming Teng
5   Pharmacological Institute, College of Medicine, National Taiwan University, Taipei, Taiwan
› Author Affiliations

Financial support: This work was supported by grants from National Science Council of Taiwan (NSC 91-2320-B-037-059).
Further Information

Publication History

Received 17 February 2003

Accepted after revision 02 May 2003

Publication Date:
06 December 2017 (online)

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Summary

There are two protease-activated receptors (PARs), PAR1 and PAR4, in human platelets. It has been suggested that PAR1 mediates platelet responses to low concentrations of thrombin, whereas PAR4 mediates signaling only at high concentrations. In the present study, we used a selective PAR4 blocker, YD-3, to investigate the role of PAR4 in thrombin-induced thromboxane formation in human platelets. YD-3 completely prevented thromboxane production by either a low concentration of thrombin (0.1 U/ml) or the PAR4 agonist peptide GYPGKF. In contrast, YD-3 did not affect thromboxane production caused by the PAR1 agonist peptide SFLLRN, collagen or arachidonic acid. YD-3 also decreased [3H]arachidonic acid release from thrombin-stimulated platelets. Moreover, desensitization of platelets with GYPGKF prevented low thrombin-induced thromboxane formation. The decreased thromboxane production by YD-3 is linked to inhibition of calcium influx in thrombin-stimulated platelets. These results suggest that PAR4 plays an important role in the regulation of thromboxane formation in platelets responding to thrombin through prolonged elevation of [Ca2+]i and activation of phospholipase A2. These data also indicate that PAR4 can be activated by relatively low concentrations of thrombin in human platelets. The selective inhibition of thrombin-induced thromboxane production by YD-3 may be of therapeutic benefit for thrombotic diseases.