Purinergic receptors on blood platelets

Extracellular adenine nucleotides interact with P2 purinergic receptors to regulate a broad range of physiological processes among which platelet aggregation P2 purinoceptors were divided into two main groups: the G-protein coupled receptor or 'metabotropic' superfamily termed P2Y and the ligand-gated ion channel or 'ionotropic receptor' superfamily termed P2X. Platelet aggregation by ADP plays a key role in the development and extension of arterial thrombosis. At present, despite a great deal of investigation aimed at assessing the central role of ADP in haemostasis, the platelet ADP receptor or so-called P(2T) purinoceptor remains basically unknown. Attempts to achieve its cloning have to date been unsuccessful and in addition more than one purinoceptor would appear to be involved in the multiple effects of ADP on platelets. The aim of this review is to try to begin to find an initial answer to the questions of how do platelets respond to ADP and what receptors are involved in these processes. A model of at least two receptors, one responsible for rapid Ca(2+) entry which could be a P(2×1) receptor and one responsible for aggregation and inhibition of adenylyl cyclase which could be a P(2Y1) receptor is proposed.