title: Nitric oxide specifically inhibits integrin-mediated platelet adhesion and spreading on collagen.
abstract: BACKGROUND
  Nitric oxide (NO) inhibits platelet adhesion to collagen, although the precise molecular mechanisms underlying this process are unclear.
  
  
  OBJECTIVE
  Collagen-mediated adhesion is a multifaceted event requiring multiple receptors and platelet-derived soluble agonists. We investigated the influence of NO on these processes.
  
  
  RESULTS
  S-nitrosoglutathione (GSNO) induced a concentration-dependent inhibition of platelet adhesion to immobilized collagen. Maximal adhesion to collagen required platelet-derived ADP and TxA(2). GSNO-mediated inhibition was lost in the presence of apyrase and indomethacin, suggesting that NO reduced the availability of, or signaling by, ADP and TxA(2). Exogenous ADP, but not the TxA(2) analogue U46619, reversed the inhibitory actions of GSNO on adhesion. Under adhesive conditions NO inhibited dense granule secretion but did not influence TxA(2) generation. These data indicated that NO may block signaling by TxA(2) required for dense granule secretion, thereby reducing the availability of ADP. Indeed, we found TxA(2)-mediated activation of PKC was required to drive dense granule secretion, a pathway that was inhibited by NO. Because our data demonstrated that NO only inhibited the activation-dependent component of adhesion, we investigated the effects of NO on individual collagen receptors. GSNO inhibited platelet adhesion and spreading on alpha(2)beta(1) specific peptide ligand GFOGER. In contrast, GSNO did not inhibit GPVI-mediated adhesion to collagen, or adhesion to the GPVI specific ligand, collagen related peptide (CRP).
  
  
  CONCLUSIONS
  NO targets activation-dependent adhesion mediated by alpha(2)beta(1), possibly by reducing bioavailability of platelet-derived ADP, but has no effect on activation-independent adhesion mediated by GPVI. Thus, NO regulates platelet spreading and stable adhesion to collagen.
authors.affiliation: Centre for Atherothrombosis Research, Medical Biosciences, University of Bradford, Bradford, UK.
authors.forename: W
authors.initials: W
authors.lastname: Roberts
authors.forename: R
authors.initials: R
authors.lastname: Riba
authors.forename: S
authors.initials: S
authors.lastname: Homer-Vanniasinkam
authors.forename: R W
authors.initials: RW
authors.lastname: Farndale
authors.forename: K M
authors.initials: KM
authors.lastname: Naseem
mesh_terms: D000244:Adenosine Diphosphate; D001792:Blood Platelets / Q000737:chemistry / Q000166:cytology; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D006801:Humans; D038982:Integrin alpha2beta1 / Q000378:metabolism; D016023:Integrins / Q000378:metabolism*; D009569:Nitric Oxide / Q000494:pharmacology*; D010455:Peptides; D010973:Platelet Adhesiveness / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D026422:S-Nitrosoglutathione / Q000494:pharmacology; D013928:Thromboxane A2
chemical_list: D038982:Integrin alpha2beta1; D016023:Integrins; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D003094:Collagen