Immuno-Localization of the Insulin Regulatable Glucose Transporter in Brown Adipose Tissue of the Rat

• Published in: The Journal of cell biology 1991-04, Vol.113 (1), p.123-135
• Main Authors: Slot, Jan W., Geuze, Hans J., Gigengack, Sander, Lienhard, Gustav E., James, David E.
• Format: Article
• Language: English
• Subjects: Adipocytes; adipose tissue (brown); Adipose Tissue, Brown - metabolism; Albumins; Animals; Biological and medical sciences; Brown adipocytes; Cell Membrane - metabolism; Cell membranes; Cell physiology; Cells; Endocytosis; Endosomes; Endothelial cells; Exocytosis; Facilitative glucose transport proteins; Fundamental and applied biological sciences. Psychology; glucose transporter; Insulin; Insulin - pharmacology; Intracellular Membranes - metabolism; Male; Microscopy, Electron; Molecular and cellular biology; Monosaccharide Transport Proteins - immunology; Monosaccharide Transport Proteins - metabolism; Rats; Rats, Inbred Strains; Vacuoles
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.113.1.123

Antibodies specific for the insulin-regulatable glucose transporter (GLUT 4) were used to immunolocalize this protein in brown adipose tissue from basal- and insulin-treated rats. Cryosections of fixed tissue were incubated with antibodies, which were subsequently labeled with Protein A/gold and examined by EM. Antibodies against albumin and cathepsin D were also used with gold particles of different sizes to identify early and late endosomes, respectively. Under basal conditions 99% of the GLUT 4 labeling was located within the cell. Labeling was predominantly in the trans-Golgi reticulum and tubulo-vesicular structures elsewhere in the cytoplasm. In insulin-stimulated cells ∼40% of the GLUT 4 labeling was at the cell surface, where it was randomly distributed, except for occasional clustering in coated pits. Moreover, after insulin treatment, GLUT 4 was also enriched in early endosomes. We conclude that translocation of GLUT 4 to the cell surface is the major mechanism by which insulin increases glucose transport. In addition, these results suggest that in the presence of insulin GLUT 4 recycles from the cell surface, probably via the coated pit-endosome pathway that has been characterized for cell surface receptors, and also that insulin causes the redistribution of GLUT 4 by stimulating exocytosis from GLUT 4-containing tubulo-vesicular structures, rather than by slowing endocytosis of GLUT 4.