Chloride conductance and sodium-dependent glucose transport in rat and human enterocytes

In cystic fibrosis intestine, there is an increase in the rate of Na+-dependent glucose absorption. This may result from enterocyte hyperpolarization after defective Cl- channel function, but only if Cl- secretion and Na+/glucose cotransport occur in the same membrane. This study examined the effects of Cl- gradients on Na+/glucose uptake in brush border membrane vesicles from rat and human small intestine.

Vesicles were prepared by Mg2+-precipitation, and the active uptake of tritiated glucose was measured using a filtration-stop protocol.

An outwardly directed Cl- gradient inhibited active glucose uptake in rat vesicles, whereas an inward Cl- gradient stimulated uptake. These effects were sensitive to blockers of the cystic fibrosis transmembrane regulator but not to inhibitors of other Cl- channels. Active glucose uptake into vesicles prepared from normal human intestine was also inhibited by an outward Cl- gradient, whereas uptake into vesicles prepared from a single sample of human cystic fibrosis intestine was not.

A Cl- conductance resembling the cystic fibrosis transmembrane regulator is colocalized with Na+/glucose cotransport in rat and human small intestine, supporting the possibility that abnormalities in glucose absorption in cystic fibrosis may be a secondary effect of defects in Cl- channel function.