A Role of the Fast ATP-gated P2X1 Cation Channel in Thrombosis of Small Arteries In Vivo

Abstract

The P2X1 receptor is a fast ATP-gated cation channel expressed in blood platelets, where its role has been difficult to assess due to its rapid desensitization and the lack of pharmacological tools. In this paper, we have used P2X1 −/− and wild-type mouse platelets, treated with apyrase to prevent desensitization, to demonstrate the function of P2X1 in the response to thrombogenic stimuli. In vitro, the collagen-induced aggregation and secretion of P2X1-deficient platelets was decreased, as was adhesion and thrombus growth on a collagen-coated surface, particularly when the wall shear rate was elevated. In vivo, the functional role of P2X1 could be demonstrated using two models of platelet-dependent thrombotic occlusion of small arteries, in which blood flow is characterized by a high shear rate. The mortality of P2X1 −/− mice in a model of systemic thromboembolism was reduced and the size of mural thrombi formed after a laser-induced vessel wall injury was decreased as compared with normal mice, whereas the time for complete thrombus removal was shortened. Overall, the P2X1 receptor appears to contribute to the formation of platelet thrombi, particularly in arteries in which shear forces are high.

P2 receptors and platelet function

“…Although unable to trigger platelet aggregation by itself, the P2X 1 receptor induces transient shape change [13] and participates in collagenand shear-induced aggregation [86][87][88]. A comprehensive review of its role in platelet function is provided by Martyn Mahaut-Smith (this issue).…”

“…In contrast, they display resistance to the systemic thromboembolism induced by injection of a mixture of collagen and adrenaline and to localized laser-induced injury of the vessel wall of mesenteric arteries [88]. Since in vitro the P2X 1 receptor plays an important role in thrombus formation only under high shear conditions, it might represent the ideal target for an antithrombotic drug.…”

Historical perspective on ADP-induced platelet activation

“…This aggregation was found to require von Willebrand factor multimers, extracellular calcium (Ca 2+ ), ADP released from the platelets, fibrinogen, and platelet membrane glycoproteins GPIbα and αIIbβ3 [71,72]. More recently, the P2X 1 receptor, stimulated by ATP released from platelets, has been shown to be required for shear-induced aggregation [73][74][75]. It has also now been found that blocking the P2Y 1 receptor for ADP prevents stabilization of aggregation [76,77].…”

“…They used transgenic mice overexpressing the P2X 1 receptor in the megakaryocyte cell lineage and found that their platelets showed enhanced aggregation and secretion in response to collagen, compared with platelets from wild-type mice. Hechler and colleagues [75] showed that platelets from mice deficient in the P2X 1 receptor had a decreased aggregation response to collagen and were protected from arterial thrombosis.…”

Molecular defects of the platelet P2 receptors

“…Platelet activation by ATP amplifies the platelet responses to other agonists, especially in flow conditions that are characterized by high shear stress [18][19][20][21][22].…”