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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1996;16:868-877.)
© 1996 American Heart Association, Inc.

Articles

Uptake of vWF–Anti-vWF Complexes by Platelets in Suspension

J.G. White; M.D. Krumwiede; D.J. Cocking-Johnson; G. Escolar

the Departments of Laboratory Medicine and Pathology, Pediatrics, University of Minnesota Medical School, Minneapolis (J.G.W., M.D.K., D.J.C.-J.), and Servicio de Hemoterapia y Hemostasia, Hospital Clinico y Provincial, Barcelona, Spain (G.E.).

Correspondence to James G. White, MD, Departments of Laboratory Medicine and Pathology, Pediatrics, University of Minnesota Medical School, 420 Delaware St SE, UMHC Box 490, Minneapolis, MN 55455.

Efforts to identify the translocation of glycoprotein (GP) Ib/IX receptors, either bound to von Willebrand factor (vWF) or not, from exposed surfaces to interior membranes of thrombin-activated platelets in suspension have been unsuccessful. To observe vWF uptake by platelets, we added an anti-vWF antibody and staphylococcal protein A–gold (to act as a marker for the antibody) to an incubation medium containing washed platelets and bovine plasma vWF or ristocetin-activated human vWF. Thin sections of platelets incubated for 10, 20, or 30 minutes with vWF but without antibody revealed no internalization and minimal changes in the original discoid form. Over the same 30-minute period with anti-vWF, however, GPIb/IX-vWF–anti-vWF complexes were cleared from cell exteriors to channels of the open canalicular system. Engorgement of the open canalicular system with vWF multimers resulted in changes in shape, internal transformation, and degranulation. Physical changes associated with anti-vWF–induced uptake of vWF are not seen in platelets that are involved in hemostatic plug formation or clot retraction.

Key Words: vWF–anti-vWF complexes • platelets • GPIb/IX • staphylococcal protein A–gold • open canalicular system