title: Insulin induces an increase in cytosolic glucose levels in 3T3-L1 cells with inhibited glycogen synthase activation.
abstract: Glucose is an important source of energy for mammalian cells and enters the cytosol via glucose transporters. It has been thought for a long time that glucose entering the cytosol is swiftly phosphorylated in most cell types; hence the levels of free glucose are very low, beyond the detection level. However, the introduction of new fluorescence resonance energy transfer-based glucose nanosensors has made it possible to measure intracellular glucose more accurately. Here, we used the fluorescent indicator protein (FLIPglu-600µ) to monitor cytosolic glucose dynamics in mouse 3T3-L1 cells in which glucose utilization for glycogen synthesis was inhibited. The results show that cells exhibit a low resting cytosolic glucose concentration. However, in cells with inhibited glycogen synthase activation, insulin induced a robust increase in cytosolic free glucose. The insulin-induced increase in cytosolic glucose in these cells is due to an imbalance between the glucose transported into the cytosol and the use of glucose in the cytosol. In untreated cells with sensitive glycogen synthase activation, insulin stimulation did not result in a change in the cytosolic glucose level. This is the first report of dynamic measurements of cytosolic glucose levels in cells devoid of the glycogen synthesis pathway.
authors.affiliation: Celica, Biomedical, Tehnološki park 24, 1000 Ljubljana, Slovenia. helena.chowdhury@mf.uni-lj.si.
authors.forename: Helena H
authors.initials: HH
authors.lastname: Chowdhury
authors.affiliation: Celica, Biomedical, Tehnološki park 24, 1000 Ljubljana, Slovenia. marko.kreft@mf.uni-lj.si.
authors.forename: Marko
authors.initials: M
authors.lastname: Kreft
authors.affiliation: Department of Physical Performance, Norwegian School of Sports Sciences, P.O. Box N-4014 Ullevål Stadion, 0806 Oslo, Norway. jorgen.jensen@nih.no.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Jensen
authors.affiliation: Celica, Biomedical, Tehnološki park 24, 1000 Ljubljana, Slovenia. robert.zorec@celica.si.
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015374:Biosensing Techniques; D004789:Enzyme Activation / Q000187:drug effects; D031541:Fluorescence Resonance Energy Transfer; D005947:Glucose / Q000032:analysis / Q000378:metabolism*; D006006:Glycogen Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D036103:Nanotechnology
chemical_list: D007328:Insulin; D008164:Luminescent Proteins; D006006:Glycogen Synthase; D005947:Glucose