Potentiation of platelet activation through the stimulation of P2X 1 receptors

Abstract

The platelet P2X 1 purinergic receptor is a ligand-gated ion channel that responds to ATP. The precise role of P2X 1 in platelet function is unknown, though stimulation with the P2X 1 agonist α,β-Me-ATP is known to result in platelet shape change through elevation of calcium levels. The aim of the present study was to examine further the effects of P2X 1 stimulation on platelet activation. Stimulation of P2X 1 with α,β-Me-ATP resulted in shape change and small aggregate formation in heparin-anticoagulated platelet preparations. Gi-ven the ability of heparin to potentiate platelet activation, subsequent experiments were performed in hirudin. In these platelet preparations, aggregate formation in response to α,β-Me-ATP alone was less than that observed in heparin; however, α,β-Me-ATP significantly potentiated platelet aggregate for-mation when added in conjunction with other weak platelet agonists [epinephrine or thrombopoietin (TPO)]. Platelet ag-gregate formation was confirmed by single platelet loss (micro-aggregate formation), microscopy, and light transmittance studies. Further, the P2X 1 antagonist MRS-2159 inhibited platelet shape change and aggregation responses induced by α,β-Me-ATP. Overall, this study demonstrates that P2X 1 sti-mulation can induce/potentiate platelet activation in combina-tion with other platelet agonists. These results are the first demonstration of platelet aggregation mediated through direct P2X 1 stimulation, supporting a role for this receptor in regulat-ing platelet activation. © 2003 International Society on Thrombosis and Haemostasis.