title: Receptor-ligand complexes are cleared to the open canalicular system of surface-activated platelets.
abstract: Human platelets were incubated with gold particles coupled to fibrinogen to label the glycoprotein IIb-IIIa (GPIIb-IIIa) receptor after initial activation of the cells by contact with formvar-coated grid and glass surfaces. Fibrinogen-gold (Fgn-Au) markers were absent on discoid platelets, but diffusely spread over the surface and extended pseudopods of early dendritic cells. Conversion to spread platelets resulted in movement of ligand-receptor complexes away from the cell margin toward cell centres. However, Fgn-Au gold did not concentrate in the central region. Rather, the Fgn-Au, GPIIb-IIIa complexes in the middle of spread platelets appeared to move toward a belt-like, intermediate zone, as did the ligand receptor complexes from the cell margin and pseudopods. The ultimate destination of the mobile receptor-ligand complexes, however, appeared to be channels of the surface-connected open canalicular system (OCS). Fgn-Au was concentrated in OCS channels of most dendritic and a small proportion of spread platelets. The decreased frequency of Fgn-Au filled channels in more transformed platelets may have been due to collapse or evagination of the OCS. Examination of platelets exposed to Fgn-Au after spreading on glass and then prepared for thin sections confirmed that the OCS was the final destination for mobile ligand receptor complexes on surface-activated platelets. Findings of this study are consistent with previous work showing clearance of mobile receptor-ligand complexes to the OCS of platelets activated in suspension.
authors.affiliation: Department of Pediatrics, Wayne State University School of Medicine, Detroit, Michigan.
authors.forename: E A
authors.initials: EA
authors.lastname: Leistikow
authors.forename: M I
authors.initials: MI
authors.lastname: Barnhart
authors.forename: G
authors.initials: G
authors.lastname: Escolar
authors.forename: J G
authors.initials: JG
authors.lastname: White
mesh_terms: D001792:Blood Platelets / Q000276:immunology* / Q000648:ultrastructure; D005340:Fibrinogen / Q000378:metabolism; D006046:Gold / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008854:Microscopy, Electron; D015539:Platelet Activation / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic / Q000378:metabolism*
chemical_list: D008024:Ligands; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011971:Receptors, Immunologic; C032193:glycoprotein receptor GPIb-IX; D006046:Gold; D005340:Fibrinogen