Sodium-Independent Uptake of Sugars by Brain-Cortex Slices

Experiments with the ventriculo-cisternal perfusion system in rabbits have shown that part of the extraction of [14C]glucose and 14C-labelled non-metabolizable glucose analogues from the perfusion system is Na+-dependent (Bradbury & Brerndsted, 1973). From this system in vivo sugars may be taken up by brain cells (neurones and glial cells) or they may pass into the circulating blood by crossing the choroid plexus or the bloodbrain barrier. To investigate whether the localization of the Na+-dependent transport mechanism is cellular the uptake by brain-cortex slices of two sugar analogues, 3methoxyglucose and a-methylglucoside was studied by using media with normal and low Na+ concentration. These sugar analogues are not metabolized by brain-cortex slices (H. E. Brmdsted, H. Lund-Andersen, C. S. Kjeldsen & L. Hertz, unpublished work). Rat brain-cortex slices of 0.5-O.6mm thickness were obtained as described by Franck et al. (1968). Incubation under intense oxygenation (Lund-Andersen & Hertz, 1970) was carried out in test tubes containing 4ml of a medium containing: l lSm~-NaCl , 2 0 m ~ NaHC03, ~ ~ M K C I , 1.4m~-CaCI,, 1.0mM-MgS04, 4m~-gh1cose and either 2 m ~ 3 methoxyglucose or 2m~-a-methylglucoside. In media with low Na+ concentration the NaCl was replaced by an equimolar amount of choline chloride. The uptake experiments (Fig. 1) were carried out as follows: after 60min of preincubation 1OpCi of either 3-O-methyl-~-['~C]ghcose, specific radioactivity 5-lOrnCil