Evidence for a sodium-dependent sugar transport in rat tracheal epithelium

The presence of Na(+)-coupled sugar transport in rat trachea was investigated using the nonmetabolizable glucose analogs methyl alpha-glucopyranoside and 3-O-methylglucose. The rates of disappearance from tracheal instillates and the tissue uptake of these analogs were compared with those of L-glucose. Experiments were performed in vivo, using a cross-circulation preparation, and in vitro, on tracheal strips. The analog methyl alpha-glucopyranoside was removed in vivo from the tracheal lumen faster than L-glucose. The cellular uptake in vivo or in vitro was determined by lysing the cells lining the tracheal lumen with detergents. This uptake was inhibited by luminal glucose, phloridzin and Na+ substitution with choline. The transport rate of 3-O-methylglucose was very low and thus discouraged inhibition experiments. These results indicate the presence of a Na+/sugar cotransport system in rat trachea. The effects of luminal interactions suggest that the cotransport is located in the apical membrane of the tracheal epithelium. It resembles that previously described in the rat alveolar epithelium, but apparently differs from that found in the fetal sheep lung in which a significant 3-O-methylglucose cotransport with Na+ has been described.