title: Molecular mechanisms involved in human platelet aggregation by synergistic interaction of platelet-activating factor and 5-hydroxytryptamine.
abstract: Our recent studies have shown that co-activation of Gq and Gi proteins by 5-hydroxytryptamine (5-HT) and adrenaline show synergism in human platelet aggregation. This study was conducted to examine the mechanism(s) of synergistic interaction of 5-HT and platelet activating factor (PAF) in human platelets. We show that PAF, but not 5-HT, increased platelet aggregation in a concentration-dependent manner. However, low concentrations of 5-HT (2 microM) potentiated platelet aggregation induced by subthreshold concentration of PAF (40 nM) indicating a synergistic interaction between the two agonists and this synergism was blocked by receptor antagonists to either 5-HT or PAF. 5-HT also potentiated the effect of PAF on thromboxane A2 (TXA2) formation and phosphorylation of extracellularly regulated mitogen-activated protein kinases (ERK1/2). The synergism of 5-HT and PAF in platelet aggregation was inhibited by calcium (Ca2+) channel blockers, verapamil and diltiazem, phospholipase C (PLC) inhibitor, U73122, cyclooxygenase (COX) inhibitor, indomethacin, and MEK inhibitor, PD98059. These data suggest that synergistic effect of 5-HT and PAF on human platelet aggregation involves activation of PLC/Ca2+, COX and MAP kinase pathways.
authors.affiliation: Department of Biological and Biomedical Sciences, The Aga Khan University, Karachi, Pakistan.
authors.forename: B H
authors.initials: BH
authors.lastname: Shah
authors.forename: H
authors.initials: H
authors.lastname: Rasheed
authors.forename: I H
authors.initials: IH
authors.lastname: Rahman
authors.forename: A H
authors.initials: AH
authors.lastname: Shariff
authors.forename: F L
authors.initials: FL
authors.lastname: Khan
authors.forename: H B
authors.initials: HB
authors.lastname: Rahman
authors.forename: S
authors.initials: S
authors.lastname: Hanif
authors.forename: S A
authors.initials: SA
authors.lastname: Saeed
mesh_terms: D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004963:Estrenes / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007700:Kinetics; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010972:Platelet Activating Factor / Q000494:pharmacology*; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects* / Q000502:physiology; D011760:Pyrrolidinones / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D013928:Thromboxane A2 / Q000096:biosynthesis; D014700:Verapamil / Q000494:pharmacology
chemical_list: D004963:Estrenes; D005419:Flavonoids; D010972:Platelet Activating Factor; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D012701:Serotonin; D013928:Thromboxane A2; D014700:Verapamil; D020928:Mitogen-Activated Protein Kinases; D004110:Diltiazem; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D007213:Indomethacin