The platelet P2X1 receptor : its activation by physiological agonists and potential as an antithrombotic target

This thesis shows that secondary activation of the P2X1 receptor represents a significant pathway by which a number of major platelet can elicit a rapid [Ca2+]I increase, particularly at weak agonist levels. P2X1 receptor activation was able to amplify the early [Ca2+]I increase evoked by collagen, thrombin, thromboxane A2 and ADP, without requiring synergy wit co-activated P2Y receptors. Moreover, contrasting the prostacyclin-sensitivity of the GPCR-coupled Ca2+-mobilisation pathways that are activated by thrombin, thromboxane A2 and ADP, the P2X1 receptor was completely insensitive to prostacyclin – a major natural platelet inhibitor that is released from the endothelium and acts to increase interplatelet cyclic AMP (cAMP). Furthermore, the early collagen-evoked [Ca2+]I response consisted of both cAMP-sensitive and –insensitive Ca2+- mobilisation components, with a Ca2+ influx through the activated P2X1 receptor representing the major contributor to the cAMP-insensitive component. Evidence suggested that early collagen-evoked ATP secretion was responsible for activating the P2X1 receptor, particularly since this nucleotide is known to be stored at high concentrations in secretory granules and activates this ionotropic receptor with high efficacy (EC50 1 receptor was unable to amplify the early collagen-evoked ATP secretion, it augmented the reversible collagen-stimulated shape change response monitored by standard turbidimetric measurements. A study of platelets stored under Blood Bank conditions found that P2X1 receptor signalling was still functional up to 14 days ex vivo, indicating that the P2X1 concentrates into a patient and that stored platelets could be a useful source of tissue to study this Ca2+-elevating receptor.EThOS - Electronic Theses Online ServiceGBUnited Kingdo