Exp Mol Med.  1999 Mar;31(1):42-46.

Co-activation of Gi and Gq proteins exerts synergistic effect on human platelet aggregation through activation of phospholipase C and Ca2+ signalling pathways

• Shah BH
• Siddiqui A
• Qureshi KA
• Khan M
• Rafi S
• Ujan VA
• Yakoob MY
• Rasheed H
• Saeed SA

Abstract

Our previous studies have shown that subthreshold concentrations of two platelet agonists exert synergistic effects on platelet aggregation. Here we studied the mechanism of synergistic interaction of 5-hydroxytryptamine (5-HT) and epinephrine mediated platelet aggregation. We show that 5-HT had no or little effect on aggregation but it did potentiate the aggregation response of epinephrine. The synergistic interaction of 5-HT (1-5 microM) and epinephrine (0.5-2 microM) was inhibited by alpha2-adrenoceptor blocker (yohimbine; IC50= 0.4 microM), calcium channel blockers (verapamil and diltiazem with IC50 of 10 and 48 mM, respectively), PLC inhibitor (U73122; IC50=6 microM) and nitric oxide (NO) donor, SNAP (IC50=1.6 microM)). The data suggest that synergistic effects of platelet agonists are receptor-mediated and occur through multiple signalling pathways including the activation PLC/Ca2+ signalling cascades.

Keyword

platelet Aggregation; phospholipase C; calcium channel blockers; epinephrine; 5-hydroxytryptamine

MeSH Terms

Blotting, Western
Calcium Channel Blockers/pharmacology
Calcium Signaling*
Drug Synergism
Enzyme Activation
Enzyme Inhibitors/pharmacology
Epinephrine/pharmacology
G-Protein, Inhibitory Gi/metabolism*
GTP-Binding Proteins/metabolism*
Human
Phospholipase C/metabolism*
Phospholipase C/antagonists & inhibitors
Platelet Aggregation/physiology
Platelet Aggregation/drug effects*
Serotonin/pharmacology
Signal Transduction