title: Effects of wortmannin on insulin- and ischemia-induced stimulation of GLUT4 translocation and FDG uptake in perfused rat hearts.
abstract: OBJECTIVE
  Myocardial glucose transport is enhanced by hormonal and other stimuli such as ischemia and hypoxia which induce glucose transporter 4 (GLUT4) translocation. Whether insulin and ischemia share a common signaling mechanism is not yet known. This study investigated whether phosphatidylinositol 3-kinase (PI3K), a signaling intermediate of the insulin-responsible pathway, also participates in the ischemia-induced stimulation of glucose.
  
  
  METHODS
  Isolated Langendorff-perfused Sprague-Dawley rat hearts were subjected to 100 nmol/l insulin or 15 min of no-flow ischemia with/without 1 mumol/l wortmannin, an inhibitor of PI3K. After perfusion, relative subcellular glucose transporter GLUT4 distribution was assessed by membrane fractionation and immunoblotting and compared to controls. Uptake kinetics of the glucose analog [18F]fluoro-deoxyglucose (FDG) were also studied during perfusion of rat hearts.
  
  
  RESULTS
  GLUT4 translocation to the plasma membrane (PM) was increased by insulin 1.8-fold and by ischemia 2.4-fold (P < 0.05). FDG uptake was increased by insulin 6.0-fold and by ischemia 6.2-fold (P < 0.05). Wortmannin 1 mumol/l inhibited insulin-mediated translocation of GLUT4 and increase in FDG uptake completely. However, it did not show any effect on ischemia-stimulated GLUT4 translocation or on ischemia-induced increase in FDG utilization. A significant correlation was found between relative GLUT4 translocation and FDG uptake in hearts of the insulin series (r = 0.9, P < 0.05) and of the ischemia series (r = 0.8, P < 0.05).
  
  
  CONCLUSIONS
  Our results demonstrate that wortmannin did not inhibit ischemia-induced stimulation of myocardial glucose transport, supporting the hypothesis of different signaling pathways for ischemia and insulin.
authors.affiliation: Klinikum rechts der Isar, Technische Universität, Munich, Germany. Silvia.Egert@lrz.tu-muenchen.de
authors.forename: S
authors.initials: S
authors.lastname: Egert
authors.forename: N
authors.initials: N
authors.lastname: Nguyen
authors.forename: F C
authors.initials: FC
authors.lastname: Brosius
authors.forename: M
authors.initials: M
authors.lastname: Schwaiger
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics; D051275:Glucose Transporter Type 4; D015151:Immunoblotting; D007329:Insulin Antagonists / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D017202:Myocardial Ischemia / Q000378:metabolism*; D010477:Perfusion; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D005462:Fluorine Radioisotopes; D051275:Glucose Transporter Type 4; D007329:Insulin Antagonists; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; C495694:Slc2a4 protein, rat; D019788:Fluorodeoxyglucose F18; D000077191:Wortmannin