myo-Inositol Transport in Mouse Astroglia-Rich Primary Cultures

Uptake of radiolabeled myo-inositol was studied in astroglia-rich primary cultures derived from neonatal mouse brains. The uptake was saturable in the presence of Na+ with a Km of 25 microM and a Vmax of 60 pmol.min-1.(mg protein)-1, suggesting a high-affinity transport system for myo-inositol in astroglial cells. In addition, a Na(+)-independent, nonsaturable component was found. Carrier-mediated uptake was not inhibited by cytochalasin B (50 microM), but was reduced by depolarizing concentrations of K+ and, to different extents, in the presence of phloretin, ouabain, or amiloride (1 mM each). scyllo-Inositol, glucose, and galactose also reduced myo-inositol uptake; inhibition by the two hexoses was not reversed in the presence of 0.4 mM sorbinil. On the other hand, uptake of 2-deoxyglucose was not inhibited by high concentrations of myo-inositol. Preincubation of the cells with glucose-free or inositol-free medium stimulated uptake of myo-inositol and preincubation with 25 mM glucose in the presence of 0.4 mM sorbinil had no effect on the rate of uptake. The results suggest that myo-inositol is taken up into the astroglial cells by a transport mechanism that is distinct from that of glucose and probably is an active one. Sorbitol pathway activity does not interfere with myo-inositol uptake.