title: L-alanine absorption in human intestinal Caco-2 cells driven by the proton electrochemical gradient.
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.
authors.affiliation: Department of Physiological Sciences, University of Newcastle upon Tyne, Medical School, UK.
authors.forename: D T
authors.initials: DT
authors.lastname: Thwaites
authors.forename: G T
authors.initials: GT
authors.lastname: McEwan
authors.forename: C D
authors.initials: CD
authors.lastname: Brown
authors.forename: B H
authors.initials: BH
authors.lastname: Hirst
authors.forename: N L
authors.initials: NL
authors.lastname: Simmons
mesh_terms: D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D001667:Binding, Competitive; D001693:Biological Transport, Active; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D011522:Protons
chemical_list: D000596:Amino Acids; D011522:Protons; D000409:Alanine