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

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 µM) and epinephrine (0.5-2 µM) was inhibited by α2-adrenoceptor blocker (yohimbine; IC50= 0.4 µM), calcium channel blockers (verapamil and diltiazem with IC50 of 10 and 48 mM, respectively), PLC inhibitor (U73122; IC50=6 µM) and nitric oxide (NO) donor, SNAP (IC50=1.6 µM)). 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.

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