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 language | English |
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Pages (from-to) | 143-51 |
Number of pages | 9 |
Journal | Journal of Membrane Biology |
Volume | 140 |
Issue number | 2 |
Publication status | Published - Jun 1994 |
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