A Possible Mechanism of Insulin Resistance in the Rat Adipose Cell with High-Fat/Low-Carbohydrate Feeding: Depletion of Intracellular Glucose Transport Systems

The effects of high-fat/low-carbohydrate feeding on glucose transport activity and on the concentrations of glucose transport systems in the plasma and low-density microsomal membranes in isolated rat adipose cells have been examined. Glucose transport activity was assessed by measuring 3-O-methylglucose transport and the concentration of glucose transport systems estimated by measuring specific D-glucose-inhibitable cytochalasin B-binding. Basal glucose transport activity is not significantly influenced by high-fat/low-carbohydrate relative to low-fat/high-carbohydrate feeding and is accompanied by a constant 10 pmol of glucose transport systems/mg of membrane protein in the plasma membrane fraction. In contrast, maximally insulin-stimulated glucose transport activity decreases from 4.72 to 2.29 fmol/cell/min and is accompanied by a decrease from 44 to 26 pmol of glucose transport systems/mg of plasma membrane protein. These diminished effects of insulin on glucose transport activity and the concentration of glucose transport systems in the plasma membrane fraction are paralleled by a 48% decrease in the basal number of glucose transport systems/mg of membrane protein in the low-density microsomal membrane fraction, the source of those glucose transport systems appearing in the plasma membrane in response to insulin. Thus, the "insulin-resistant" glucose transport of the adipose cell with high-fat/low-carbohydrate feeding may be the consequence of a depletion of glucose transport systems in the intracellular pool.