3-O-methyl-D-glucose uptake in isolated rat hepatocytes. Effects of dexamethasone

We examined the uptake of 3-O-methyl-D-glucose, a nonmetabolizable hexose, by isolated rat hepatocytes. The uptake of 3-O-methyl-D-glucose was linear for 1 min at 22°, and Lineweaver-Burk analysis demonstrated an apparent K(m) of ~6 mM. Cytochalasin B (40 μM) and phloridzin (2 mM) inhibited 3-O-methyl-D-glucose uptake by 88% and 63%, respectively. D-Glucose (20 mM) inhibited the initial rate of 3-O-methyl-D-glucose uptake by 55% (P < 0.001), whereas L-glucose was without any significant effect. The uptake of 3-O-methyl-D-glucose remained unchanged in the presence of Na⁺ (0-150 mM) in the incubation medium. After 30 min dexamethasone inhibited glucose uptake (the maximal effect being achieved in a time- and concentration-dependent manner) at 2 μM and 0.5 μM concentrations by 50% and 25%, respectively. Dexamethasone produced a decrease in the V(max) but did not change the K(m). Insulin, glucagon, gastric inhibitory polypeptides, and pancreozymin had no effect on 3-O-methyl-D-glucose uptake in isolated hepatocytes. These findings are consistent with the conclusion that 3-O-methyl-D-glucose uptake in isolated rat hepatocytes occurs via a stereospecific, carrier-mediated, facilitated diffusion process. Dexamethasone decreases this process of facilitated diffusion in the isolated hepatocyte.