title: Quantitative ultrastructural, autoradiographic evidence for the magnitude and early involvement of the Golgi apparatus complex in the endocytosis of wheat germ agglutinin by cultured neuroblastoma.
abstract: Several ligands undergo endocytosis into the Golgi apparatus. We have examined with a quantitative ultrastructural, autoradiographic method the sequential endocytosis of tritiated wheat germ agglutinin (3H-WGA) by cultured murine neuroblastoma cells. Cells were incubated with 3H-WGA for 1 hour at 4 degrees C, washed, and incubated in complete medium without ligand at 37 degrees C for 5, 15, 30, and 120 minutes. At 5 minutes, the optimized sources/micron 2 of neuroblastoma cell area, which represented the grain density of each compartment, were as follows: smooth vesicles and tubules, 1.03 +/- 0.88; Golgi-associated vesicles, i.e., clusters of vesicles within a 1 micron radius of the Golgi cisterns, 1.03 +/- 0.31; Golgi cisterns, less than 0.01; and lysosomes, 0.26 +/- 0.16. At 15 minutes grain densities were: smooth vesicles and tubules, 0.9 +/- 0.34; Golgi-associated vesicles, 1.41 +/- 0.28; Golgi cisterns, 0.73 +/- 0.41; and lysosomes, 0.1 +/- 0.09. At 30 minutes grain densities were: smooth vesicles and tubules, 0.46 +/- 0.46; Golgi-associated vesicles, 1.78 +/- 0.34; Golgi cisterns, 0.89 +/- 0.78; and lysosomes, 0.39 +/- 0.14. At 2 hours, smooth vesicles, tubules, and Golgi cisterns were not labeled, Golgi-associated vesicles were still labeled (0.71 +/- 0.1), and lysosomes were heavily labeled (2.17 +/- 0.22). These results are consistent with the hypotheses that either the Golgi complex (cisterns and associated vesicles) is an early and intermediate step of the endocytosis of 3H-WGA into lysosomes or that it constitutes part of a separate and quantitatively significant pathway of endocytosis of this ligand.
mesh_terms: D000818:Animals; D001345:Autoradiography; D002460:Cell Line; D002478:Cells, Cultured; D004705:Endocytosis; D005293:Ferritins; D006056:Golgi Apparatus / Q000648:ultrastructure*; D006735:Horseradish Peroxidase / Q000378:metabolism; D008854:Microscopy, Electron; D009447:Neuroblastoma / Q000378:metabolism / Q000648:ultrastructure*; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins / Q000378:metabolism*
chemical_list: D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins; D005293:Ferritins; D006735:Horseradish Peroxidase