Confocal microscopy study of the different patterns of 2-NBDG uptake in rabbit enterocytes in the apical and basal zone

D-Glucose uptake in isolated rabbit enterocytes was studied using confocal microscopy and 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glu cose (2-NDBG), a D-glucose fluorescent analogue, by analysing the fluoresce nce of apical and basal enterocyte zones. Under normal conditions, apical f luorescence was always higher than basal, presumably due to the location of the Na+-D-glucose cotransporter in the brush-border membrane. After blocki ng this transporter with phlorizin, apical and basal fluorescence values we re similar. This suggests that both brush-border and basolateral membranes participate in phlorizin-insensitive D-glucose transport, since transport a cross only one membrane cannot explain the uniform overall fluorescence obs erved. Similarly, after inhibiting the Na+-D-glucose cotransporter by incub ating the enterocytes in a medium containing 0.5 mM Na+, neither apical nor basal fluorescence predominated. In contrast, with 130.5 mM extracellular Na+, apical fluorescence was clearly higher than basal fluorescence. These results suggest that phlorizin-insensitive, Na+-independent 2-NDBG uptake o ccurred through both brush-border and basolateral membranes, probably via t he glucose uniporters GLUT2 and GLUT5, suggesting that the latter is a D-gl ucose transporter.