Fibrinogen (Fg) mediates platelet aggregation and adhesion to artificial surfaces by interacting with its receptor, glycoprotein IIb and IIIa complex (GPIIbIIIa, or integrin alphaIIbbeta 3), on the platelet membrane. Considerable evidence has demonstrated that the (H12) on the gamma chain carboxyl terminus is required for the binding of Fg from solution to activated platelet GPIIbIIIa, while the RGD sites, the universal integrin recognition domain on adhesive ligands, are not involved. In this study, using recombinant Fg, well-defined Fg plasmin digestion fragments, and specific monoclonal anit-Fg antibodies, we demonstrated that the same sequence, the H12, or more precisely, the AGDV on the extreme carboxyl terminus of the gamma chain (gamma408--411), is also required for platelet-bound Fg to support platelet aggregation (crosslinking), thus experimentally verifying the "two sticky ends" theory of Fg-mediated platelet aggregation The RGD-containing domains on the Aalpha chains are not involved in aggregation. The AGDV sequence on the gamma chain carboxyl terminus is also necessary and sufficient for activated platelets to adhere to surface-adsorbed Fg, while the RGD sequences we similarly not required. A receptor induced binding site (RIBS), the Fg RIBS-I site (gamma373--385), on Fg either bound to its GPIIbIIIa-receptor or on a surface, is not directly involved in interactions between platelet GPIIbIIIa and immobilized Fg. The inhibitory effects of the anti-Fg-RIBS-I antibody are due to steric hindrance of the accessibility of the AGDV site to platelet GPIIbIIIa. Thus, the extreme carboxyl terminus of the gamma chain is the only site in both fluid and solid phase Fg that is involved in platelet GPIIbIIIa-Fg interactions. / Though resting platelets are able to adhere to surface-bound Fg, this adhesion efficiency is much lower than that of the adhesion of the activated platelets. The adhesion efficiency of both resting and activated platelets to surface-adsorbed Fg decreases with increasing shear rate from 100 s -1 to 2,000 s-1. However, the decrease of the adhesion efficiency of the resting platelets is more marked than the decrease of the adhesion efficiency of the activated ones. Thus, the higher the shear rates, the larger the difference in the adhesion efficiencies between resting and activated platelets. However, due to the higher collision frequencies at higher shear rates, the adhesion of resting platelets was maintained at a similar level from shear rates of 300--2,000 s-1, while the adhesion of activated platelets kept increasing from 100 s -1 to 2,000 s-1. These data indicate that platelet activation is an efficient regulation pathway for platelet adhesion to surfaces.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35909 |
| Date | January 1998 |
| Creators | Liu, Qingde, 1963- |
| Contributors | Frojmovic, Mony M. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001650979, proquestno: NQ50213, Theses scanned by UMI/ProQuest. |
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