Influence of Protein Kinase C and Calcium in the Course of Thrombin Receptors Activation.

Object In order to compare the functions of protein kinase C (PKC) and calcium (Ca²⁺) in platelet aggregation and platelet membrane surface glycoproteins GPIb expression after thrombin receptors activation, then to investigate the role of Gq signal transmission pathway in the course of thrombin receptors activation.

Methods Peptide SFLLRN (PAR1-AP) and AYPGKF (PAR4-AP) were used for stimulating platelet at different time point (0, 1, 2, 5, 10, 30min), then the alterations of platelet aggregation and GPIb were analyzed in the involvement of Ro-31-2220 (inhibitor of PKC) and BAPTA/AM (calcium chelator).

Results Either PAR1 or PAR4 peptide can induce absolute platelet aggregation, together with a reversible internalization of GPIb. Platelet aggregation was inhibited by Ro-31-2220 or BAPTA/AM while the shape change curve still occurred upon PARs activation. In addition, Ro-31-2220 decreases GPIb centralisation upon PAR1 stimulation (P <0.05 at 1, 2 min), though it blocks the pool of GPIb inside platelet in PAR4 activation (P <0.05 at 10, 30 min). Meanwhile, GPIb internalization was blocked by BAPTA for both peptides (P <0.05 at 1∼10 min).

Conclusion All the results confirm a critical role of Gq pathway in thrombin signal transmission through the involvement of protein kinase C and calcium. Calcium is closely correlated with the thrombin receptors activation, seemed to be similar for two PARs signal pathways. Protein kinase C urges GPIb centralisation in PAR1 pathway and accelerates GPIbα return in PAR4 pathway.