UPTAKE OF 3‐O‐METHYL‐d‐GLUCOSE INTO CULTURED HUMAN GLIOMA CELLS

— Human glioma cells (138 MG) were found to take up 3-O-methyl-d-glucose (3-OMG) by a saturable low affinity transport system with a Km of 20 mm and a Vmax of 500 nmol/mg protein/min. About 20 per cent of the total uptake was due to passive diffusion. d-Glucose was a competitive inhibitor with a Ki of 10 mm. Follow-up experiments indicated that the same transport mechanism is involved in the uptake of n-glucose and 3-OMG. Phloretin (0·02 mm) and cytochalasin B (0·002 mm) strongly inhibited the uptake of 3-OMG, whereas phlorizin (0·02 mm), ouabain (0·1 mm), NaCN (0·5 mm) and iodoacetic acid (1·0 mm) had no effect. The data suggest that 3-OMG and d-glucose enter 138 MG cells mainly by a Na+-independent passive carrier-mediated transport system. Serum-deprivation doubled the population doubling time (Td) without affecting the total uptake of 3-OMG. An increase in the non-specific (diffusional) uptake was balanced by a decrease in the specific (carrier-mediated) uptake. After addition of dibutyryl cyclic AMP (dbcAMP, 0·25 mm) the cells attained a morphology characteristic of differentiated glia cells. Td was maintained unchanged. The non-specific uptake of 3-OMG was not affected in cells grown in serum-containing medium plus dbcAMP, whereas the specific uptake increased by 40 per cent and there-fore also the total uptake. Similar, but more pronounced, changes were observed if serum-deprived cells were treated with dbcAMP.