Relative Effectiveness of Extracellular and Intracellular Sodium in Supporting Leucine Uptake by Isolated Intestinal Epithelial Cells 1

Summary

The effects of changes in the extracellular as well as the intracellular Na concentrations on the movement of leucine into or out of isolated intestinal epithelial cells was determined. The influx of leucine was optimal at an initial extracellular Na⁺ concentration of 118 mM despite variations in the intracellular Na⁺ concentration over the range 8-122 mM. The influx of leucine was decreased 40% when the initial extracellular Na⁺ concentration was zero and the magnitude of the reduced influx was not affected by initial intracellular Na⁺ concentrations over the range 57-122 mM. Leucine movement into or out of leucine-loaded cells followed the direction of the Na⁺-gradient across the cell membrane. These results indicate that extracellular rather than intracellular Na⁺ is the determining factor in the Na⁺ dependence of leucine transport, a finding consistent with the Na⁺-gradient hypothesis for amino acid transport.

The authors thank Loutitia Ferdinandus and William Heaton for their valuable technical assistance.