Sodium ion transport in isolated intestinal epithelial cells. The effect of actively transported sugars on sodium ion efflux

Abstract

A technique to measure Na + efflux from isolated intestinal epithelial cells has permitted us to examine the mechanisms responsible for Na + transport in absorptive cells without contamination by other cell types. We examined the effect of actively transported sugars on Na + efflux from isolated rat jejunal epithelial cells to evaluate the mechanism by which actively transported non-electrolytes stimulate Na + absorption. Glucose, galactose and 3-O- methylglucose , sugars known to be actively transported by the small intestine, stimulate total Na + efflux from isolated epithelial cells. This stimulation results from an increase of active Na + transport, since it is inhibited by ouabain. Glucose stimulation is significantly greater than that produced by galactose or 3-O- methylglucose , 2-Deoxyglucose, a sugar that is not actively transported, has no effect on total Na + efflux from isolated cells. Phloridzin, which has no effect on Na + efflux in a sugar-free medium, completely abolishes the effect of galactose. These findings (a) support the hypothesis that the increase in intestinal absorption of Na + in the presence of actively transported non-electrolytes occurs by a transcellular route; and (b) are consistent with the ion-gradient model. The results are not compatible with the direct energy-coupling model.