title: Insulin stimulates the halting, tethering, and fusion of mobile GLUT4 vesicles in rat adipose cells.
abstract: Glucose transport in adipose cells is regulated by changing the distribution of glucose transporter 4 (GLUT4) between the cell interior and the plasma membrane (PM). Insulin shifts this distribution by augmenting the rate of exocytosis of specialized GLUT4 vesicles. We applied time-lapse total internal reflection fluorescence microscopy to dissect intermediates of this GLUT4 translocation in rat adipose cells in primary culture. Without insulin, GLUT4 vesicles rapidly moved along a microtubule network covering the entire PM, periodically stopping, most often just briefly, by loosely tethering to the PM. Insulin halted this traffic by tightly tethering vesicles to the PM where they formed clusters and slowly fused to the PM. This slow release of GLUT4 determined the overall increase of the PM GLUT4. Thus, insulin initially recruits GLUT4 sequestered in mobile vesicles near the PM. It is likely that the primary mechanism of insulin action in GLUT4 translocation is to stimulate tethering and fusion of trafficking vesicles to specific fusion sites in the PM.
authors.affiliation: Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Lizunov
authors.forename: Hideko
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Joshua
authors.initials: J
authors.lastname: Zimmerberg
authors.forename: Samuel W
authors.initials: SW
authors.lastname: Cushman
authors.forename: Vadim A
authors.initials: VA
authors.lastname: Frolov
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D005947:Glucose