Abstract
Transepithelial apical-to-basal transport and cellular uptake of the non-metabolisable amino acid alpha-methylaminoisobutyric acid (MeAIB) across confluent monolayers of the human intestinal epithelial cell line Caco-2 are enhanced by a transepithelial pH gradient (apical pH 6.0, basolateral pH 7.4). In Na(+)-free conditions (apical pH 7.4, basolateral pH 7.4), net absorption (120 +/- 58 pmol/cm2 per h, n = 13) and uptake across the apical membrane (cell/medium ratio 0.56 +/- 0.06, n = 13) are low. However, in Na(+)-free conditions with apical pH 6.0, net absorption (685 +/- 95 pmol/cm2 per h, n = 15) and intracellular accumulation (cell/medium ratio 3.63 +/- 0.29, n = 14) were marked. Continuous monitoring of intracellular pH (pHi) in BCECF (2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein)-loaded Caco-2 cell monolayers indicated that apical addition of MeAIB (20 mM) was associated with H(+)-flow across the apical membrane in both Na+ and Na(+)-free conditions. This transport process is rheogenic in Na(+)-free media, stimulating an inward short-circuit current in voltage-clamped Caco-2 cell monolayers. On the basis of competition for MeAIB accumulation and pHi experiments, L-proline, glycine, L-alanine and beta-alanine are also substrates for H(+)-linked transport at the apical membrane of Caco-2 cells but L-valine, L-leucine and L-phenylalanine are not. These data are consistent with the expression, in the apical brush-border membrane of Caco-2 cells, of a H(+)-coupled, Na(+)-independent MeAIB carrier.
Original language | English |
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Pages (from-to) | 111-8 |
Number of pages | 8 |
Journal | Biochimica et Biophysica Acta |
Volume | 1234 |
Issue number | 1 |
Publication status | Published - 8 Mar 1995 |
Keywords
- Biological Transport
- Cell Line
- Cell Polarity
- Cytoplasm
- Epithelium
- Humans
- Hydrogen-Ion Concentration
- Intestinal Absorption
- Intestinal Mucosa
- Intestines
- Patch-Clamp Techniques
- Sodium
- beta-Alanine