Related Experiment Videos
Subcellular platelet factor VIII antigen and von Willebrand factor
Abstract:
Subcellular membrane and granule fractions derived from human platelets contain factor VIIII antigen and von Willebrand factor activity but not factor VII procoagulant activity. Circulating platelets constitute a significant reservoir of plasma factor VIII antigen, containing approximately 15% of the amount of factor VIII antigen present in platelet-poor plasma. The antibiotic ristocetin, which aggregates human platelets in the presence of von Willebrand factor, nonspecifically precipitates platelet membrane factor VIII antigen. Thus normal platelets contain surface-bound as well as internally stored von Willebrand factor, a protein synthesized by endothelial cells which is necessary for normal platelet function in vivo.
Insights
Human platelets store von Willebrand factor (vWF) antigen, essential for platelet function. Platelets contain both surface-bound and internal vWF, with ristocetin aggregating platelets by precipitating membrane-bound vWF antigen.
Area of Science:
- Hematology
- Cell Biology
- Biochemistry
Background:
- Platelets play a crucial role in hemostasis and thrombosis.
- Von Willebrand factor (vWF) is essential for normal platelet adhesion and aggregation.
- Factor VIII antigen is found in various biological fractions.
Purpose of the Study:
- To investigate the presence and localization of factor VIII antigen and von Willebrand factor activity in human platelet fractions.
- To determine if platelets contain factor VII procoagulant activity.
- To elucidate the role of platelets as a reservoir for plasma proteins.
Main Methods:
- Fractionation of human platelets into subcellular membrane and granule components.
- Assay for factor VIII antigen.
- Measurement of von Willebrand factor activity.
- Assessment of factor VII procoagulant activity.
- Ristocetin-induced platelet aggregation studies.
Main Results:
- Subcellular fractions of human platelets contain factor VIII antigen and von Willebrand factor activity.
- Platelets do not contain factor VII procoagulant activity.
- Circulating platelets store approximately 15% of the factor VIII antigen found in platelet-poor plasma.
- Ristocetin nonspecifically precipitates platelet membrane-bound factor VIII antigen, indicating surface-bound vWF.
- Normal platelets contain both internally stored and surface-bound von Willebrand factor.
Conclusions:
- Human platelets serve as a significant reservoir for factor VIII antigen and von Willebrand factor.
- Von Willebrand factor is present both internally and on the surface of platelets.
- Platelet-associated von Willebrand factor is crucial for normal platelet function in vivo.