A study of P2X(1) receptor function in murine megakaryocytes and human platelets reveals synergy with P2Y receptors

1 We have examined the role of ATP-dependent P2X(1) receptors in megakaryocytes (MKS) and platelets using receptor-deficient mice and selective agonists. 2 alpha,beta-meATP- and ATP- evoked ionotropic inward currents were absent in whole-cell recordings frorn MKS of P2X(1)(-/-) mice, demonstrating that the P2X receptor phenotype in MKs, and by inference, platelets, is due to expression of homomeric P2X(1) receptors. 3 P2X(1) receptor deficiency had no effect on MK (CD 41) numbers or size distribution, showing that it is not essential for normal MK development. 4 P2Y receptor-stimulated [Ca2+](i) responses were unaffected in MKs from P2X(1)(-/-) mice, however the inward cation current associated with Ca2+ release was reduced by similar to50%, suggesting an interaction between the membrane conductances activated by P2X(1) and P2Y receptors. 5 Interaction between P2X(1) and P2Y receptors in human platelets was also examined using [Ca2+](i) recordings from cell suspensions. alpha,beta-meATP (10 muM) evoked a rapid transient P2X(1) receptor-mediated increase in [Ca2+](i), whereas ADP-(10 muM) evoked P2Y receptor responses were slower, peaked at a higher level and remained elevated for longer periods. Co-application of alpha,beta-meATP and ADP resulted in marked acceleration and amplification of the peak [Ca2+](i) response. 6 We conclude that ionotropic P2X(1) receptors may play a priming role in the subsequent activation of metabotropic P2Y receptors during platelet stimulation.