Influx and efflux of 3-O-methyl-D-glucose by cultured human fibroblasts.

We measured the initial rates of 3-O-methyl-D-glucose (OMG) fluxes by cultured human fibroblasts. D-Glucose (300 mM) and cytochalasin B (5 microM) inhibited approximately 80% of OMG (1 mM) influx. OMG rapidly entered human fibroblasts, and influx was linear up to 20 s. OMG influx and efflux were about equal. Cytochalasin B inhibited OMG (1 mM) influx and efflux within 20 s of exposure. Cytochalasin B half maximally inhibited OMG influx and efflux at 0.51 and 0.75 microM, respectively. In zero trans conditions, the kinetics of OMG influx and efflux were similar. However, when OMG was present on the trans side of the membrane, OMG influx but not OMG efflux was stimulated. Trans stimulation of OMG influx increased the maximal velocity of this transport process, without affecting its Km. These results suggest that 1) OMG influx and efflux occur through the same transporter, and 2) the glucose transporter of cultured human fibroblasts presents a functional asymmetry when substrate is present on the trans side of the membrane.