Techniques to Examine Platelet Adhesive Interactions Under Flow
Platelet adhesion and aggregation at sites of vessel-wall injury are critical for the arrest of bleeding and for the development of vaso-occlusive thrombi at sites of atherosclerotic-plaque rupture. These adhesive interactions are critically dependent on multiple receptors on the platelet surface (GPIb/V/IX, GPVI, integrins αIIbβ3 and α2β1) and their specific ligands in the subendothelium (von Willebrand Factor, collagen) and plasma (von Willebrand Factor, fibrinogen) (1,2). In vivo, these receptor-ligand interactions are exposed to a broad range of shear stresses generated by blood flow, ranging from 20–200/s in veins to 800–10,000/s in arteries (3). In stenotic vessels, shear rates can approach 40,000/s. The development of in vitro methodologies mimicking physiological and pathophysiological flow conditions has significantly improved our understanding of the role of shear in regulating platelet functional responses. In general, the effects of shear stress have been studied with platelets in suspension using rotational devices such as the Couette or cone-plate viscometer. Alternatively, the effects of shear on platelets have been evaluated in a laminar-flow device such as the tubular, annular, or parallel-plate flow chamber. Rotational viscometers are ideal for the examination of shear effects on platelet adhesive interactions in the absence of platelet-surface interactions (i.e., platelets in suspension). Such studies are important in determining the mechanisms of platelet activation occurring in areas of vascular stenosis where shear rates are elevated well above physiological levels. Thrombus formation, however, does not generally occur with platelets in suspension but rather involves the progressive accrual of platelets onto vascular subendothelium and subsequently onto immobilized platelets. As such, the in vitro investigation of platelet function under conditions of physiological and pathological shear has been greatly facilitated by laminar flow devices.
KeywordsShear Rate Platelet Adhesion Platelet Thrombus Thrombus Growth Microcapillary Tube
- 11.Moake, J. L., Turner, N. A., Stathopoulos, N. A., Nolasco, L. H., and Hellums, J. D. (1986) Involvement of large plasma von Willebrand factor (vWF) multimers and unusually large vWF forms derived from endothelial cells in shear stress-induced platelet aggregation. J. Clin. Invest. 78, 1456–1461.PubMedCrossRefGoogle Scholar
- 12.Moake, J. L., Turner, N. A., Stathopoulos, N. A., Nolasco, L. H., and Hellums, J. D. (1988) Shear-induced platelet aggregation can be mediated by vWF released from platelets, as well as by exogenous large or unusually large vWF multimers, requires adenosine diphosphate, and is resistant to aspirin. Blood 71, 1366–1374.PubMedGoogle Scholar
- 14.Cazanave, J. P., Hemmendinger, S., Beretz, A., Sutter-Bay, A., and Launay, J. (1983) L’agrégation plaquettaire: outil d’investigation clinique et d’étude pharmacologique méthodologie. Ann. Biol. Clin. 41, 167–179.Google Scholar
- 17.Yap, C. L., Hughan, S. C., Cranmer, S. L., Nesbitt, W. S., Rooney, M. M., Giuliano, S., et al. (2000) Synergistic adhesive interactions and signaling mechanisms operating between platelet glycoprotein Ib/IX and integrin αIIbβ3. Studies in human platelets and transfected chinese hamster ovary cells. J. Biol. Chem. 275, 41,377–41,388.PubMedCrossRefGoogle Scholar