title: Cytochalasin D and E: effects on fibrinogen receptor movement and cytoskeletal reorganization in fully spread, surface-activated platelets: a correlative light and electron microscopic investigation.
abstract: This study investigates the involvement of actin microfilaments in fibrinogen receptor redistribution and cytoskeletal reorganization that takes place in fully spread, surface-activated platelets. Colloidal gold-labeled fibrinogen (Fgn-Au label) in conjunction with video-enhanced differential interference contrast light microscopy (VDIC) was used to identify fibrinogen binding sites, glycoprotein IIb/IIIb (GPIIb/IIIa), on fully spread platelets. Platelets were treated with cytochalasins D and E (5 x 10(-5) mol/L to 5 x 10(-8) mol/L) for 10 minutes, before or after incubation with Fgn-Au label. Results observed with VDIC were subsequently confirmed by high-voltage transmission and low voltage-high resolution scanning electron microscopic examination of the specimens. Preincubation of activated platelets with cytochalasin D or E (5 x 10(-5) and 5 x 10(-6) mol/L) inhibited fibrinogen receptor redistribution and abolished cytoskeletal reorganization in fully spread platelets. After surface-activated platelets were incubated with Fgn-Au label, treatment with the above concentrations of cytochalasin D or E disrupted cytoskeletal reorganization and caused random movement of previously redistributed receptor-ligand complexes. Incubation of platelets with cytochalasin E 5 x 10(-6) mol/L prevented platelet activation and spreading. Thus, actin filaments appear necessary for platelet spreading from the discoid to the fully spread stage. The ligand-triggered, cytoskeletally directed movement of fibrinogen receptors in fully spread platelets appears to be dependent on the presence of intact, polymerized actin. This movement is distinct from the cytochalasin-insensitive accumulation of GPIIb/IIIa-ligand in the channels of the open canalicular system.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Ilorin, Nigeria.
authors.forename: O E
authors.initials: OE
authors.lastname: Olorundare
authors.forename: S R
authors.initials: SR
authors.lastname: Simmons
authors.forename: R M
authors.initials: RM
authors.lastname: Albrecht
mesh_terms: D000199:Actins / Q000097:blood; D000328:Adult; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D003102:Colloids; D015638:Cytochalasin D / Q000494:pharmacology*; D003572:Cytochalasins / Q000494:pharmacology*; D003599:Cytoskeleton / Q000378:metabolism*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D006046:Gold; D006801:Humans; D008853:Microscopy; D008854:Microscopy, Electron; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D014741:Video Recording
chemical_list: D000199:Actins; D003102:Colloids; D003572:Cytochalasins; D010980:Platelet Membrane Glycoproteins; D015638:Cytochalasin D; C007215:cytochalasin E; D006046:Gold; D005340:Fibrinogen; D004121:Dimethyl Sulfoxide