title: Evidence for functionally distinct glucose transporters in basal and insulin-stimulated adipocytes.
abstract: The activity and Km of glucose transport of rat adipocytes are quite variable in the basal state. This could be due to differing levels of highly saturable transport against a background of less saturable transport. Such heterogeneity could lead to differing conclusions as to the Km of basal cells compared to insulin-stimulated cells depending on the choice of substrate, the range of concentrations tested, and the rigor of data analysis. In the present work, we used a cell preparation which was stable and partially activated by constant agitation. We used a two-component model to fit the concentration dependence of D-glucose uptake. We defined two parallel pathways of glucose entry, a high-affinity/low-capacity pathway and a low-affinity/high-capacity pathway. Both pathways were stereospecific and were inhibited by cytochalasin B. The low-affinity pathway in basal cells had 97% of the total capacity (Vmax) with a high Km (greater than 50 mM). A second pathway had a very low Km (less than 1 mM) and only 3% of the total capacity, but contributed to 30-60% of glucose uptake at 8 mM glucose. In insulin-stimulated cells, a pathway with a Km of 4-5 mM dominated and contributed 85% of glucose transport. The low-affinity but not the very high affinity pathway persisted in stimulated cells, but its contribution was only 10-15% of transport at 8 mM glucose. These results suggest the presence of at least two functionally distinct transporters whose respective contributions can be characterized by nonlinear regression of data over a wide range of glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: R R
authors.initials: RR
authors.lastname: Whitesell
authors.forename: D M
authors.initials: DM
authors.lastname: Regen
authors.forename: N A
authors.initials: NA
authors.lastname: Abumrad
mesh_terms: D019325:3-O-Methylglucose; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D051381:Rats; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D007328:Insulin; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D014316:Tritium; D019325:3-O-Methylglucose; D005947:Glucose