L-alanine absorption in human intestinal Caco-2 cells driven by the proton electrochemical gradient

D T Thwaites, G T McEwan, C D Brown, B H Hirst, N L Simmons

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Abstract

In human Caco-2 intestinal epithelial layers, L-alanine absorption can be energized by a proton gradient across the brush-border membrane. Acidification of the apical medium, even in Na(+)-free media, is associated with a saturable net transepithelial absorption of L-alanine. L-Alanine transport causes cytosolic acidification consistent with proton/amino acid symport. L-Alanine transport in Na(+)-free media is rheogenic, stimulating an inward short-circuit current in voltage-clamped epithelial monolayers. By measurement of rapid L-alanine influx across the apical membrane, L-alanine-stimulated inward short-circuit current and intracellular acidification in the same cell batch, we estimate L-alanine/proton stoichiometry to be 1:0.62 +/- 0.25 (SD) (short-circuit current) or 1:0.73 +/- 0.19 (intracellular acidification). From competition studies, it is likely that L-proline, alpha-aminoisobutyric acid, and beta-alanine, but not L-valine and L-serine, are substrates for proton-linked, substrate transport in the brush border of Caco-2 cells.
Original languageEnglish
Pages (from-to)143-51
Number of pages9
JournalJournal of Membrane Biology
Volume140
Issue number2
Publication statusPublished - Jun 1994

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Keywords

  • Alanine
  • Amino Acids
  • Binding, Competitive
  • Biological Transport, Active
  • Cell Line
  • Cell Membrane
  • Electrochemistry
  • Epithelium
  • Humans
  • Hydrogen-Ion Concentration
  • Intestinal Absorption
  • Intestines
  • Intracellular Fluid
  • Microvilli
  • Protons

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