title: A revised model of platelet aggregation.
abstract: In this study we have examined the mechanism of platelet aggregation under physiological flow conditions using an in vitro flow-based platelet aggregation assay and an in vivo rat thrombosis model. Our studies demonstrate an unexpected complexity to the platelet aggregation process in which platelets in flowing blood continuously tether, translocate, and/or detach from the luminal surface of a growing platelet thrombus at both arterial and venous shear rates. Studies of platelets congenitally deficient in von Willebrand factor (vWf) or integrin alpha(IIb)beta(3) demonstrated a key role for platelet vWf in mediating platelet tethering and translocation, whereas integrin alpha(IIb)beta(3) mediated cell arrest. Platelet aggregation under flow appears to be a multistep process involving: (a) exposure of vWf on the surface of immobilized platelets; (b) a reversible phase of platelet aggregation mediated by the binding of GPIbalpha on the surface of free-flowing platelets to vWf on the surface of immobilized platelets; and (c) an irreversible phase of aggregation dependent on integrin alpha(IIb)beta(3). Studies of platelet thrombus formation in vivo demonstrate that this multistep adhesion mechanism is indispensable for platelet aggregation in arterioles and also appears to promote platelet aggregate formation in venules. Together, our studies demonstrate an important role for platelet vWf in initiating the platelet aggregation process under flow and challenge the currently accepted view that the vWf-GPIbalpha interaction is exclusively involved in initiating platelet aggregation at elevated shear rates.
authors.affiliation: Australian Centre for Blood Diseases, Department of Medicine, Monash Medical School, Box Hill Hospital, Box Hill, Victoria 3128, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Kulkarni
authors.forename: S M
authors.initials: SM
authors.lastname: Dopheide
authors.forename: C L
authors.initials: CL
authors.lastname: Yap
authors.forename: C
authors.initials: C
authors.lastname: Ravanat
authors.forename: M
authors.initials: M
authors.lastname: Freund
authors.forename: P
authors.initials: P
authors.lastname: Mangin
authors.forename: K A
authors.initials: KA
authors.lastname: Heel
authors.forename: A
authors.initials: A
authors.lastname: Street
authors.forename: I S
authors.initials: IS
authors.lastname: Harper
authors.forename: F
authors.initials: F
authors.lastname: Lanza
authors.forename: S P
authors.initials: SP
authors.lastname: Jackson
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018056:Hemorheology; D006801:Humans; D008954:Models, Biological; D010973:Platelet Adhesiveness / Q000502:physiology; D010974:Platelet Aggregation / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics / Q000502:physiology; D051381:Rats; D013915:Thrombasthenia / Q000097:blood; D013927:Thrombosis / Q000209:etiology / Q000503:physiopathology; D014162:Transfection; D014842:von Willebrand Diseases / Q000097:blood; D014841:von Willebrand Factor / Q000502:physiology*
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor