title: Agonist and antagonist effects of diadenosine tetraphosphate, a platelet dense granule constituent, on platelet P2Y1, P2Y12 and P2X1 receptors.
abstract: BACKGROUND
  Diadenosine 5',5'''-P(1),P(4)- tetraphosphate (Ap(4)A) is stored in platelet dense granules, but its effects on platelet function are not well understood.
  
  
  RESULTS
  We examined the effects of Ap(4)A on platelet purinergic receptors P2Y(1), P2Y(12) and P2X(1). Flow cytometry was used to measure the effects of Ap(4)A in the presence or absence of ADP on: a) P2Y(12)-mediated decrease in intraplatelet phosphorylated vasodilator stimulated phosphoprotein (VASP), b) P2Y(1)-mediated increase in platelet cytosolic Ca(2+), and c) P2X(1)-mediated intraplatelet entry of extracellular Ca(2+). ADP-stimulated platelet shape change (P2Y(1)-mediated) and aggregation (P2Y(1)- and P2Y(12)-mediated) were measured optically. Ap(4)A inhibited 3 microM ADP-induced: a) platelet aggregation (IC(50) 9.8+/-2.8 microM), b) P2Y(1)-mediated shape change, c) P2Y(1)-mediated increase in platelet cytosolic Ca(2+) (IC(50) 40.8+/-12.3 microM), and d) P2Y(12)-mediated decrease in VASP phosphorylation (IC(50)>250 microM). In the absence of added ADP, Ap(4)A had agonist effects on platelet P2X(1) and P2Y(12), but not P2Y(1), receptors.
  
  
  CONCLUSIONS
  Ap(4)A, a constituent of platelet dense granules, is a) an antagonist of platelet P2Y(1) and P2Y(12) receptors, where it inhibits the effects of ADP, and b) an agonist of platelet P2X(1) and P2Y(12) receptors.
authors: Center for Platelet Function Studies, Department of Pediatrics, University of Massachusetts Medical School, Worcester, MA, USA.
authors: Hung
authors: H
authors: Chang
authors: Ivan B
authors: IB
authors: Yanachkov
authors: Alan D
authors: AD
authors: Michelson
authors: YouFu
authors: Y
authors: Li
authors: M R
authors: MR
authors: Barnard
authors: George E
authors: GE
authors: Wright
authors: Andrew L
authors: AL
authors: Frelinger
mesh_terms: D001792:Blood Platelets / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism*; D015226:Dinucleoside Phosphates / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D058469:Receptors, Purinergic P2X; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12
chemical_list: D015226:Dinucleoside Phosphates; C546382:P2RY1 protein, human; C548576:P2RY12 protein, human; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D058469:Receptors, Purinergic P2X; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; C020733:diadenosine tetraphosphate