title: Glucose transporter in bovine mammary epithelial cells is an asymmetric carrier that exhibits cooperativity and trans-stimulation.
abstract: Glucose transport kinetics were quantified in isolated bovine mammary epithelial cells using 3-O-methyl-D-glucose. Isolated cells retained satisfactory viability and glucose uptake activity, which was inhibited by cytochalasin B, phloretin, HgCl2, and low temperature. Initial rates of entry were measured over a 15-s interval at 37 degrees C under zero-trans, equilibrium-exchange, high-cis, and high-trans concentrations of 3-O-methyl-D-glucose between 0 and 20 mM. The combined set of rate measurements from all experimental conditions was fit to the fixed-site carrier model by nonlinear regression to estimate parameters of transport. For the regression between predicted and observed initial rates, r2 was 0.97. Forward Vmax was estimated at 18.2 nmol.min-1.mg protein-1, and the Michaelis constant was 8.29 mM. The cooperativity parameter was 1.63, trans-stimulation was 2.13-fold, and asymmetry was 2.06-fold. On the basis of the kinetic parameters, variations in intracellular glucose concentrations are not responsible for the range of glucose uptakes by bovine mammary glands observed in vivo.
authors.affiliation: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Changting
authors.initials: C
authors.lastname: Xiao
authors.forename: John P
authors.initials: JP
authors.lastname: Cant
mesh_terms: D019325:3-O-Methylglucose / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002469:Cell Separation; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D051272:Glucose Transporter Type 1; D007700:Kinetics; D008321:Mammary Glands, Animal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; D019325:3-O-Methylglucose