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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.

The human P2Y! purinoceptor has been expressed in Jurkat cells and the effects of HPLC purified nucleotides on calcium movements were measured. The most potent agonist was 2-methylthio-ADP followed by ADP. ATP, Sp-ATPctS and ß,^ methylene-ATP were competitive antagonists. Suramin and PPADS inhibited the effects of ADP. This pharmacological profile is the same as that of the so-called P2T purinoceptor responsible for platelet aggregation, which has not yet been identified. Using PCR we found the P2Y] receptor to be present in blood platelets and megakaryoblastic cell lines. These data suggest that the P2Yx receptor may be the elusive P2T receptor.

See also Brill A. A ride with ferric chloride. This issue, pp 776–8. Summary.  Background: The FeCl3‐induced vascular injury model is widely used to study thrombogenesis in vivo, but the processes leading to vascular injury and thrombosis are poorly defined. Objectives: The aim of our study was to better characterize the mechanisms of FeCl3‐induced vascular injury and thrombus formation, in order to evaluate the pathophysiological relevance of this model. Methods: FeCl3 was applied at different concentrations (from 7.5% to 20%) and for different time periods (up to 5 min) to mouse carotid or mesenteric arteries. Results: Under all the conditions tested, ultrastructural analysis revealed that FeCl3 diffused through the vessel wall, resulting in endothelial cell denudation without exposure of the inner layers. Hence, only the basement membrane components were exposed to circulating blood cells and might have contributed to thrombus formation. Shortly after FeCl3 application, numerous ferric ion‐filled spherical bodies appeared on the endothelial cells. Interestingly, platelets could adhere to these spheres and form aggregates. Immunogold labeling revealed important amounts of tissue factor at their surface, suggesting that these spheres may play a role in thrombin generation. Invitro experiments indicated that FeCl3 altered the ability of adhesive proteins, including collagen, fibrinogen and von Willebrand factor, to support platelet adhesion. Finally, real‐time intravital microscopy showed no protection against thrombosis in GPVI‐immunodepleted and β1−/− mice, suggesting that GPVI and β1 integrins, known to be involved in initial platelet adhesion and activation, do not play a critical role in FeCl3‐induced thrombus formation. Conclusion: This model should be used cautiously, in particular to study the earliest stage of thrombus formation.