Unidirectional influx and phosphorylation of glucose analogues in cultured astroblasts

Unidirectional influx of 14C-3OMG (3-O-methyl-D-glucose) and rate of phosphorylation of 14C-2DG (2-deoxy-D-glucose) were determined in primary cultures of astroblasts under conditions with negligible unstirred layers. The influx exhibited rate constants between 7.2 and 8.3 min-1 in the concentration range 2.5-25 mM of unlabeled 3OMG and was considered constant, irrespective of concentration of 3OMG. The rate of phosphorylation of 14C-2DG declined for rising concentrations of 2DG and hence showed saturability. The rate constants ranged from 7.9 to 0.1 min-1 in the concentration range 0.04-25 mM of 2DG. These results are not consistent with the view that the influx limits the rate of phosphorylation. They support the notion that the influx is not rate limiting for the phosphorylation.