Assembly and GPIIIa Content of Cytoskeletal Core in Platelets Agglutinated With Bovine von Willebrand Factor

The association between occupancy of the von Willebrand factor (vWf) receptor glycoprotein (GP) Ib, agglutination, and the assembly and composition of the cytoskeletal core was studied in ‘261-surface-labeled aspirin-treated washed platelets. Binding of ligands to GPllb-llla and platelet aggregation were abolished by addition of EDTA. Platelet agglutination induced by bovine vWf generated a complete cytoskeletal core (Triton-insoluble residue). shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to be composed of actin-binding protein (ABP) (260 Kd), 235-Kd protein, myosin heavy chain (200 Kd), a-actinin (100 Kd), and actin (43 Kd). In addition, autoradiography of the gels showed a lZ61 105-Kd GP. identified by immunoblot as GPllla, as well as GPlb, GPllb. and another band at 87 Kd, probably GPIV. Neither cytoskeletal assembly nor GPllla incorporation was altered if calpain was