Topographic distribution of a granule membrane protein (GMP-140) that is expressed on the platelet surface after activation: an immunogold-surface replica study.
Monoclonal and polyclonal antibodies have been developed that recognize a 140 kD glycoprotein on the plasma membrane of activated, but not unstimulated, platelets. This glycoprotein is found in resting platelets as an alpha-granule membrane protein and has therefore been named GMP-140. After thrombin stimulation, alpha-granules fuse with the surface-connected canalicular system and GMP-140 is redistributed to the plasma membrane. In the present study, we immunolabeled unstimulated and activated human platelets and analyzed the distribution of GMP-140 over broad expanses of the plasma membrane using surface replication techniques. Fixed platelets were allowed to settle onto poly-L-lysine-coated coverslips and immunolabeled with polyclonal anti-GMP-140, followed by protein A gold. After critical-point drying, rotary-shadowed surface replicas were made. GMP-140 was not present on the surfaces of unstimulated platelets, but thrombin stimulation resulted in the massive expression of GMP-140 on the cell surface, with the immunogold label monodispersed. In contrast, we recently found that GPIIb-IIIa, the fibrinogen receptor, is monodispersed on unstimulated platelets and clustered on activated platelets. Although GMP-140's hemostatic function is unknown, its monodispersed surface pattern implies significant differences form GPIIb-IIIa with respect to ligand binding and/or cytoskeletal interaction.
D001792:Blood Platelets / Q000032:analysis* / Q000187:drug effects; D002462:Cell Membrane / Q000032:analysis; D006023:Glycoproteins; D006046:Gold; D006651:Histocytochemistry; D006801:Humans; D007159:Immunologic Tests; D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins / Q000032:analysis / Q000097:blood*; D013205:Staphylococcal Protein A; D013917:Thrombin / Q000494:pharmacology
D006023:Glycoproteins; D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins; D013205:Staphylococcal Protein A; D006046:Gold; D013917:Thrombin