title: Distinct glycoprotein Ib/V/IX and integrin alpha IIbbeta 3-dependent calcium signals cooperatively regulate platelet adhesion under flow.
abstract: We have investigated the calcium signaling relationship between the two major platelet adhesion receptors, glycoprotein Ib/V/IX (GPIb/V/IX) and integrin alpha(IIb)beta(3), involved in regulating platelet adhesion on von Willebrand factor (vWf) under flow. Our studies demonstrate that GPIb engagement of immobilized vWf elicits a transient calcium spike that may function to promote reversible arrest of translocating platelets. Subsequent integrin alpha(IIb)beta(3) engagement of vWf promotes sustained calcium oscillations that are essential for the maintenance of irreversible adhesion. GPIb-induced calcium spikes appear distinct from those initiated by integrin alpha(IIb)beta(3), in that the former are exclusively mediated through release of intracellular calcium stores via a signaling mechanism independent of PI 3-kinase. In contrast, integrin alpha(IIb)beta(3)-dependent calcium flux involves a PI 3-kinase-dependent signaling mechanism linked to intracellular calcium mobilization and subsequent transmembrane calcium influx. Studies employing the caged calcium chelator (o-nitrophenyl-EGTA) demonstrate that transient calcium spikes initiate a transient phase of platelet arrest that is converted to irreversible adhesion with the development of sustained oscillatory calcium flux. These studies demonstrate the existence of a dual step calcium signaling mechanism utilized by GPIb and integrin alpha(IIb)beta(3) that serves to regulate the dynamics of platelet adhesion under flow.
authors.affiliation: Australian Centre for Blood Diseases, Monash University, Box Hill Hospital, Box Hill, Victoria 3127, Australia.
authors.forename: Warwick S
authors.initials: WS
authors.lastname: Nesbitt
authors.forename: Suhasini
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Simon
authors.initials: S
authors.lastname: Giuliano
authors.forename: Isaac
authors.initials: I
authors.lastname: Goncalves
authors.forename: Sacha M
authors.initials: SM
authors.lastname: Dopheide
authors.forename: Cindy L
authors.initials: CL
authors.lastname: Yap
authors.forename: Ian S
authors.initials: IS
authors.lastname: Harper
authors.forename: Hatem H
authors.initials: HH
authors.lastname: Salem
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Jackson
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002448:Cell Adhesion; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D002614:Chelating Agents; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D004533:Egtazic Acid; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium