title: Apical and basolateral localisation of GLUT2 transporters in human lung epithelial cells.
abstract: Glucose concentrations of normal human airway surface liquid are approximately 12.5 times lower than blood glucose concentrations indicating that glucose uptake by epithelial cells may play a role in maintaining lung glucose homeostasis. We have therefore investigated potential glucose uptake mechanisms in non-polarised and polarised H441 human airway epithelial cells and bronchial biopsies. We detected mRNA and protein for glucose transporter type 2 (GLUT2) and glucose transporter type 4 (GLUT4) in non-polarised cells but GLUT4 was not detected in the plasma membrane. In polarised cells, GLUT2 protein was detected in both apical and basolateral membranes. Furthermore, GLUT2 protein was localised to epithelial cells of human bronchial mucosa biopsies. In non-polarised H441 cells, uptake of D: -glucose and deoxyglucose was similar. Uptake of both was inhibited by phloretin indicating that glucose uptake was via GLUT-mediated transport. Phloretin-sensitive transport remained the predominant route for glucose uptake across apical and basolateral membranes of polarised cells and was maximal at 5-10 mM glucose. We could not conclusively demonstrate sodium/glucose transporter-mediated transport in non-polarised or polarised cells. Our study provides the first evidence that glucose transport in human airway epithelial cells in vitro and in vivo utilises GLUT2 transporters. We speculate that these transporters could contribute to glucose uptake/homeostasis in the human airway.
authors.affiliation: Centre for Ion Channel and Cell Signalling, Division of Basic Medical Sciences, St George's, University of London, Cranmer Terrace, London, SW17 0RE, UK.
authors.forename: Kameljit K
authors.initials: KK
authors.lastname: Kalsi
authors.forename: Emma H
authors.initials: EH
authors.lastname: Baker
authors.forename: Rodolfo A
authors.initials: RA
authors.lastname: Medina
authors.forename: Suman
authors.initials: S
authors.lastname: Rice
authors.forename: David M
authors.initials: DM
authors.lastname: Wood
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Ratoff
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Philips
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Baines
mesh_terms: D016764:Cell Polarity; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D010695:Phlorhizin / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology*
chemical_list: D051273:Glucose Transporter Type 2; D051275:Glucose Transporter Type 4; C495680:SLC2A2 protein, human; C495692:SLC2A4 protein, human; D010695:Phlorhizin; D005947:Glucose