Muscle subcellular localization and recruitment by insulin of glucose transporters and Na+-K+-ATPase subunits in transgenic mice overexpressing the GLUT4 glucose transporter.
Insulin-stimulated glucose uptake in skeletal muscle is mediated through the GLUT4 glucose transporter. Transgenic (TG) mice overexpressing human GLUT4 in skeletal muscle show an increased ability to handle a glucose load. Here, the participation of the overexpressed GLUT4 in the response to insulin was examined. In TG mouse muscle, the GLUT4 protein content was 10-fold higher in crude membrane (CM), sevenfold higher in internal membrane (IM), and 15-fold higher in a plasma membrane (PM)-rich fraction, relative to non-TG littermates. This suggested partial saturation of the normal sorting mechanisms. The distribution and abundance of the GLUT1 glucose transporter was not affected. Insulin injection (4.3 U/kg body wt) increased GLUT4 in the PM-rich fraction; the increase was threefold higher in TG than in non-TG mice. Insulin decreased the GLUT4 content of the IM in both animal groups and of a second, heavier intracellular membrane fraction only in TG mice. The net content of Na+-K+-pump subunits was 40-65% lower in CM from TG compared with non-TG littermates. In spite of this, insulin caused a three- to sixfold higher translocation of the alpha2 and beta1 subunits of the Na+-K+-pump in TG compared with non-TG animals. The results suggest that overexpression of GLUT4 confers to the muscle increased ability to translocate subunits of the Na+-K+-pump either as a direct consequence of the recruitment of glucose transporters or as an adaptation to the more demanding metabolic state.
Ramlal
T
T
Division of Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Ewart
H S
HS
Somwar
R
R
Deems
R O
RO
Valentin
M A
MA
Young
D A
DA
Klip
A
A
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D015309:Glucose Clamp Technique; D051275:Glucose Transporter Type 4; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D046911:Macromolecular Substances; D051379:Mice; D008822:Mice, Transgenic; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D012016:Reference Values; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D046911:Macromolecular Substances; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase