On the uptake of hexoses by rat cerebral cortical slices

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 Km (8.85 and 1.05 mM) and Vmax (20.41 +/- 5.99 nmol/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.

[3H]2-deoxyglucose transport by slices of cerebral cortex: apparent dependence upon mitochondrial energy

The transport of [3H]2-deoxyglucose by brain slices was studied. Cerebral cortex slices were incubated in vitro in the presence of [3H]2-deoxyglucose, or L-[3H]glucose as a marker for diffusion. Transport was defined as the difference between [3H]2DG uptake and L-[3H]glucose uptake. Half-maximal velocity was seen at 2.0 mM 2DG and [3H]2DG transport was not inhibited by 20-fold higher concentrations of L-glucose. Net [3H]2DG transport was unchanged in media deficient in Na+, K+, Mg2+, Ca2+ or Cl-. Uptake was significantly inhibited by 1.0 mM 2,4-DNP and a suggestion of inhibition by azide was seen. These data are consistent with a hypothesis that hexose transport in the brain depends to some extent upon mitochondrial energy.

Uptake of 2-deoxy-D-glucose by cortical synaptosomes from the Long-Evans rat

Uptake of 2-deoxy-D-glucose (2-DG) has been studied in synaptosomes from the Long-Evans rat. Although there are some differences, the results are generally similar to those reported for Sprague--Dawley rats. Both D-glucose and 2-DG are taken up by the same carrier, since D-glucose was found to inhibit uptake of 2-DG. Uptake is highly dependent on a source of metabolic energy, since incubation at 0 degrees C completely eliminated uptake, while 10(-3) M 2,4-dinitrophenol (DNP) inhibited uptake by 76.5%. Uptake has also been measured as a function of both 2-DG and sodium concentration and the data fitted to a model. Sodium is found to inhibit uptake. A model assuming noncompetitive inhibition by sodium gives best fit to the data. Thus both Kt and apparent Vm are dependent on the sodium concentration. Although these effects are small, Kt increases with [Na], while apparent Vm declines.

Uptake of radiolabeled glucose analogues by organotypic cerebellar cultures

Permeability of brain cells to radiolabeled glucose analogues with sucrose or inulin or L-glucose was studied in the living, intact state of the organotypic cerebellar cultures. In vitro uptake of 3H 3-O-methyl D-glucose and 3H 2-deoxy-D-glucose exhibited saturation kinetics with increasing substrate concentrations. Each of the labeled sugars uptake could be self-inhibited in the presence of unlabeled (cold) substrate and cross-inhibited with cold glucose or xylose or phlorizin present in the incubating medium. The uptake was Na-independent and stereo-specific for D-form.

Glycolytic metabolism in cultured cells of the nervous system. I. Glucose transport and metabolism in the C-6 glioma cell line

The transport and metabolism of glucose was examined in monolayers of C-6 glioma cells. 1) Glucose transport appeared to have both a low (Km = 7.74 mM) and a high (Km = 1.16 mM) affinity site in C-6cells; whereas 2-deoxyglucose had only one (Km = 3.7 mM). 2) A large portion of the accumulated glucose was rapidly metabolized to the two glycolytic end products, lactate and pyruvate, and then extruded into the medium. The temperature-dependent efflux of lactate and pyruvate was linear up to 2 hrs with 6 to 10 times more lactate being extruded into the medium than pyruvate. 3) The efflux of lactate and pyruvate increased with increasing extracellular (medium) pH. The presence of 5 percent CO2 not only inhibited the acid efflux but also inhibited the short-term uptake of glucose. The CO2 effect was attributed to a lowering of the medium pH since bicarbonate alone either increased or did not inhibit efflux. 4) Valinomycin increased the levels of cellular lactate but not those of pyruvate by almost three-fold. Lactate efflux was stimulated while that of pyruvate was inhibited. The addition of 5 percent CO2 increased the cellular levels of both lactate and pyruvate, but unlike valinomycin decreased the acid efflux. Idoacetate inhibited the acid efflux by 50 percent suggesting that glycolysis is necessary for efflux.