Glucose transport in intestinal epithelia of winter flounder

D-Glucose (Glc) transport was studied in stripped intestinal epithelial sheets of the winter flounder Pseudopleuronectes americanus. At 1 mM Glc and 15 degrees C, Glc uptake did not occur against a concentration gradient (free cell Glc 0.78 +/- 0.06 mM) but was inhibited by 0.5 mM phlorizin or ouabain. [U-14C]-Glc oxidation to 14CO2 was also depressed by these agents or the absence of Na+ and was saturable (Km 3.3 +/- 1.2 mM Glc; maximal velocity at saturating substrate concentration (Vmax) 4.0 +/- 2.0 mumol X g wet wt-1 X h-1]. No electrical transcellular manifestations of the Na-Glc cotransport system were seen in regular media. In the absence of Cl-, Glc and nonmetabolizable Glc analogs (alpha-methyl-D-glucopyranoside or 3-O-methyl-D-glucose) added mucosally elicited an increase in a serosally directed short-circuit current that was inhibitable by 0.5 mM mucosal phlorizin or 0.1 mM serosal ouabain and dependent on the external sugar concentration [Km 2.3 +/- 1.8 mM (range 0.6 to 6.1); Vmax 2.4 +/- 1.1 microA X cm-2 (range 0.8-4.2)]. Vmax for L-leucine transport was fivefold greater [13.4 +/- 7.3 microA X cm-2 (range 4.6-20.7)]. These results indicate the presence of a mucosal Na+-linked Glc absorptive system and reflect the paucity of transport sites for Glc relative to leucine.