RT Journal Article SR Electronic T1 Ca2+ Influx through P2X1 Receptors Amplifies P2Y1 Receptor-evoked Ca2+ Signalling and ADP-evoked Platelet Aggregation JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP mol.114.092528 DO 10.1124/mol.114.092528 A1 Sarah Jones A1 Richard J Evans A1 Martyn P Mahaut-Smith YR 2014 UL http://molpharm.aspetjournals.org/content/early/2014/06/12/mol.114.092528.abstract AB Many cells express both P2X cation channels and P2Y G-protein-coupled receptors that are co-stimulated by nucleotides released during physiological or pathophysiological responses. For example, during haemostasis and thrombosis, ATP-gated P2X1 channels and ADP-stimulated P2Y1 and P2Y12 G-protein coupled receptors play important roles in platelet activation. It has previously been reported that P2X1 receptors amplify P2Y1-evoked Ca2+ responses in platelets but the underlying mechanism and influence on function is unknown. In human platelets, we show that maximally activated P2X1 receptors failed to stimulate significant aggregation, but could amplify the aggregation response to a submaximal concentration of ADP. Co-stimulation of P2X1 and P2Y1 receptors generated a super-additive Ca2+ increase in both human platelets and HEK293 cells via a mechanism dependent on Ca2+ influx rather than Na+ influx or membrane depolarisation. The potentiation, due to an enhanced P2Y1 response, was observed if ADP was added up to 60 seconds after P2X1 activation. P2X1 receptors also enhanced Ca2+ responses when co-stimulated with type 1 protease activated and M1 muscarinic acetylcholine receptors. The P2X1-dependent amplification of Gq-coupled [Ca2+]i increases was mimicked by ionomycin, and not affected by inhibition of protein kinase C, Rho-kinase and ERK1/2, suggesting that it results from potentiation of IP3 receptors and/or phospholipase-C. We conclude that Ca2+ influx through P2X1 receptors amplifies Ca2+ signalling through P2Y1 and other Gq-coupled receptors. This represents a general form of co-incidence detection of ATP and co-released agonists, such as ADP at sites of vascular injury or synaptic transmitters acting at metabotropic Gq-coupled receptors.