Exp Mol Med.  2004 Jun;36(3):220-225.

Involvement of throm box aneA2 and tyrosine kinase in the synergistic interaction of platelet activating factor and calcium ionophore A23187 in human platelet aggregation

• Rasheed H
• Saeed SA

Abstract

The present study was carried out to examine the mechanisms of the synergistic interaction of PAF and A23187 mediated platelet aggregation. We found that platelet aggregation mediated by subthreshold concentrations of PAF (5 nM) and A23187 (1 micrometer) was inhibited by PAF receptor blocker (WEB 2086, IC50=0.65 micrometer) and calcium channel blockers, diltiazem (IC50=13 micrometer) and verapamil (IC50=18 micrometer). Pretreatment of platelets with PAF and A23187 induced rise in intracellular calcium and this effect was also blocked by verapamil. While examining the role of the down stream signaling pathways, we found that platelet aggregation induced by the co-addition of PAF and A23187 was also inhibited by low concentrations of phospholipase C (PLC) inhibitor (U73122; IC50 = 10 micrometer), a cyclooxygenase inhibitor (indomethacin; IC50=0.2 micrometer) and inhibitor of TLCK, herbimycin A with IC50 value of 5 micrometer. The effect was also inhibited by a specific TXA2 receptor antagonist, SQ 29548 with very low IC50 value of 0.05 micrometer. However, the inhibitors of MAP kinase, PD98059 and protein kinase C, chelerythrine had no effect on PAF and A23187-induced platelet aggregation. These data suggest that the synergism between PAF and A23187 in platelet aggregation involves activation of thromboxane and tyrosine kinase pathways.

Keyword

calcium ionophore A23187; platelet activating factor; platelet aggregation; thromboxane tyrosine kinase

MeSH Terms

Blood Platelets/*drug effects
Calcimycin/*pharmacology
Humans
Indomethacin/pharmacology
Ionophores/pharmacology
Platelet Activating Factor/metabolism/*pharmacology
Platelet Aggregation/*physiology
Protein-Tyrosine Kinase/antagonists & inhibitors/*physiology
Quinones/pharmacology
Research Support, Non-U.S. Gov't
Thromboxane A2/*physiology
Verapamil/pharmacology