title: Mechanisms of glucose uptake in intestinal cell lines: role of GLUT2.
abstract: BACKGROUND
  GLUT2 is translocated to the apical membrane of enterocytes exposed to glucose concentrations >∼50 mM. Mechanisms of GLUT2-mediated glucose uptake in cell culture models of enterocytes have not been studied.
  
  
  OBJECTIVE
  To explore mechanism(s) of glucose uptake in 3 enterocyte-like cell lines.
  
  
  METHODS
  Glucose uptake was measured in Caco-2, RIE-1, and IEC-6 cell lines using varying concentrations of glucose (0.5-50 mM). Effects of phlorizin (SGLT1 inhibitor), phloretin (GLUT2 inhibitor), nocodazole and cytochalasin B (disrupters of cytoskeleton), calphostin C and chelerythrine (PKC inhibitors), and phorbol 12-myristate 13-acetate (PKC activator) were evaluated.
  
  
  RESULTS
  Phlorizin inhibited glucose uptake in all 3 cell lines. Phloretin inhibited glucose uptake in Caco-2 and RIE-1 cells. Starving cells decreased glucose uptake in Caco-2 and RIE-1 cells. Glucose uptake was saturated at >10 mM glucose in all 3 cell lines when exposed briefly (<1 min) to glucose. After exposure for >5 min in Caco-2 and RIE-1 cells, glucose uptake did not saturate and K(m) and V(max) increased. This increase in glucose uptake was inhibited by phloretin, nocodazole, cytochalasin B, calphostin C, and chelerythrine. PMA enhanced glucose uptake by 20%. Inhibitors and PMA had little or no effect in the IEC-6 cells.
  
  
  CONCLUSIONS
  Constitutive expression of GLUT2 in the apical membrane along with additional translocation of cytoplasmic GLUT2 to the apical membrane via an intact cytoskeleton and activated PKC appears responsible for enhanced carrier-mediated glucose uptake at greater glucose concentrations (>20 mM) in Caco-2 and RIE-1 cells. IEC-6 cells do not appear to express functional GLUT2.
authors.affiliation: Department of Surgery and the Gastroenterology Research Unit, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Ye
authors.initials: Y
authors.lastname: Zheng
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Scow
authors.forename: Judith A
authors.initials: JA
authors.lastname: Duenes
authors.forename: Michael G
authors.initials: MG
authors.lastname: Sarr
mesh_terms: D018938:Caco-2 Cells; D002454:Cell Differentiation; D016764:Cell Polarity; D003599:Cytoskeleton / Q000502:physiology; D020895:Enterocytes / Q000166:cytology / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000378:metabolism*; D006801:Humans; D008286:Malabsorption Syndromes / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051269:Sodium-Glucose Transporter 1 / Q000378:metabolism
chemical_list: D051273:Glucose Transporter Type 2; C495680:SLC2A2 protein, human; C495674:SLC5A1 protein, human; D051269:Sodium-Glucose Transporter 1; D011493:Protein Kinase C; D005947:Glucose