UTILIZATION OF MANNOSE BY ASTROGLIAL CELLS

Uptake and metabolism of mannose were studied in astroglia-rich primar y cultures derived from neonatal rat brains. A saturable component of mannose uptake was found with half-maximal uptake at 6.7 +/- 1.0 mM ma nnose. In addition, a non-saturable component dominated the uptake at high concentrations of mannose. Glucose, cytochalasin B, or phloretin in the incubation buffer inhibited the carrier-mediated uptake of mann ose. Within the astroglial cells mannose is phosphorylated to mannose- 6-phosphate. In cell homogenates, the K(M) value of mannose-phosphoryl ating activity was determined to be 24 +/- 7 muM. The V(max) value of this activity is only 40% that of glucose-phosphorylating activity. Ma nnose-6-phosphate was converted to fructose-6-phosphate by mannose-6-p hosphate isomerase. The specific activity of this enzyme in homogenate s of astroglial cultures was higher than that of hexokinase. Two produ cts of mannose utilization in astroglial cells are glycogen and lactat e. The amounts of each of these products increased with increasing con centrations of mannose. In contrast to the generation of lactate, that of glycogen from mannose was enhanced in the presence of insulin. In conclusion, we suggest that mannose is taken up into the cells of astr oglia-rich primary cultures by the glial glucose transporter and is me tabolized to fructose-6-phosphate within the astroglial cells.