Transport of 2-deoxy-d-glucose by dissociated brain cells

The characteristics of glucose transport into dissociated cells from rat brain were determined using [1,2-³H]2-deoxyglucose as substrate. The rate of net uptake exhibited biphasic saturation kinetics with increasing substrate concentration; two values each for K_m (8.85 and 1.05 mM) and V_max (20.41 ± 5.99nmol/min/mg protein) were obtained, indicating the presence of two transport systems. d-glucose competed with [1,2-³H]2-deoxyglucose as shown by increasing degrees of inhibition of uptake of labeled substrate with increasing concentrations of d-glucose. The presence of an accelerative exchange mechanism was demonstrated by enhanced rates of uptake of labeled substrate by cells pre-loaded with high levels of unlabeled 2-deoxyglucose. Transport was inhibited by cytochalasin B, phloretin and phloridzin in a manner suggesting that the system is sodium-independent. Transport was also inhibited by sodium cyanide, potassium cyanide and dinitrophenol, but not by sodium arsenite or ouabain. Insulin status of the animals had no effect on the rate of transport of this substrate. Net transport was significantly lower in neonatal (4-day-old) rats than in either older sucklings (14–16-day-old) or adult animals; no significant difference between the latter two groups was observed. These findings demonstrate that two carrier-mediated systems for glucose transport are present on the membranes of these mixed brain cells suggesting that the kinetic characteristics of glucose transport may differ between neurons and glial cells. The age change in transport rate may reflect age-associated glial cell proliferation and/or an age-dependent increase in the number of transporters per cell in one brain cell type.