Immuno-localization of the insulin regulatable glucose transporter in brown adipose tissue of the rat.
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 approximately 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.
Slot
J W
JW
Department of Cell Biology, Medical School, University of Utrecht, The Netherlands.
Geuze
H J
HJ
Gigengack
S
S
Lienhard
G E
GE
James
D E
DE
D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis; D005089:Exocytosis; D007328:Insulin / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008854:Microscopy, Electron; D009004:Monosaccharide Transport Proteins / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D007328:Insulin; D009004:Monosaccharide Transport Proteins