Hexose transport in human adipocytes: factors influencing the response to insulin and kinetics of methylglucose and glucose transport.
Optimal experimental conditions were defined for measuring the initial uptake rate of the non-metabolizable sugar analogue 3-O-methylglucose in non-stimulated and insulin-stimulated human adipocytes. The permeability of the adipocyte plasma membrane for tracer methylglucose (100 mumol/l) was 2.9 X 10(-7) cm X s-1 at 37 degrees C and slightly lower at 20 degrees C. At 37 degrees C and pH 7.4 insulin (5 nmol/l) increased the permeability about twofold (range 1.5 to fivefold) with half maximal effect at about 100 pmol/l). At pH 7.0 the dose response curve for the insulin effect on the uptake rate of methylglucose was shifted about 2.5-fold to the right. The permeability to L-glucose due to simple diffusion was estimated as 3.0 X 10(-10) cm X s-1 suggesting that uptake of methylglucose occurs almost exclusively by facilitated diffusion. The Km for methylglucose equilibrium exchange in insulin stimulated cells was about 4.8 mmol/l. The initial uptake of tracer methylglucose in insulin-stimulated cells was inhibited by unlabelled methylglucose and by D-glucose with inhibition constants of about 3.8 and 7.7 mmol/l respectively. Uptake of tracer 2-deoxyglucose (50 mumol/l) in insulin-stimulated adipocytes was linear from 10 s to 5 min whereas the rate of uptake in the presence of 3 mmol/l of D-glucose was markedly decreased suggesting that deoxyglucose uptake after a few minutes is mainly limited by hexokinase in the presence of glucose.
D000273:Adipose Tissue / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001692:Biological Transport; D002463:Cell Membrane Permeability / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D003847:Deoxyglucose / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008757:Methylglucosides / Q000378:metabolism*; D008759:Methylglycosides / Q000378:metabolism*; D008875:Middle Aged; D010693:Phloretin / Q000494:pharmacology
D007328:Insulin; D008757:Methylglucosides; D008759:Methylglycosides; D003571:Cytochalasin B; D003847:Deoxyglucose; D005947:Glucose; D010693:Phloretin