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Studies on the platelet surface-associated von Willebrand factor
S E Martin1, M M Johnson, R F Abel
1Department of Pathology, Medical Center of Delaware, Newark 19718.
American Journal of Hematology
|May 1, 1994
Summary
Platelets contribute to stopping bleeding using von Willebrand factor (vWF) from their surface. Mechanical stress can expose this surface vWF, aiding platelet adhesion and clot formation.
Area of Science:
- Hematology
- Platelet Biology
- Hemostasis
Background:
- Platelets are crucial for hemostasis, relying on both plasma and platelet-derived von Willebrand factor (vWF).
- Platelet vWF is primarily stored in alpha-granules, but some is found on the platelet surface even without stimulation.
Purpose of the Study:
- To investigate the presence and characteristics of vWF on the surface of washed platelets.
- To determine if this surface vWF is dependent on specific platelet glycoproteins or intracellular calcium levels.
Main Methods:
- Washing platelets in a calcium-free medium with prostaglandin E1.
- Incubating platelets with anti-vWF F(ab')2 fragments and separating bound antibodies via gel chromatography.
- Comparing normal platelets with those from patients with Bernard Soulier syndrome, Glanzmann's thrombasthenia, and Hermansky-Pudlak syndrome.
Main Results:
- von Willebrand factor (vWF) is detectable on the surface of washed platelets in a calcium-free environment.
- This surface vWF expression is independent of glycoproteins Ib and IIb-IIIa.
- Surface vWF is present despite significantly reduced intracellular calcium.
Conclusions:
- Platelet manipulation during in vitro washing likely causes the observed surface expression of vWF.
- This mechanically induced surface vWF enhances its availability for critical platelet adhesion and aggregation interactions, particularly under high flow conditions.