PEPT1-mediated uptake of dipeptides enhances the intestinal absorption of amino acids via transport system b ^0,+

Free amino acids and short chain peptides are the main digestion products of dietary proteins in the small intestine. Whether there is a direct interference in transport of both groups of degradation products is not known. We used human intestinal Caco-2 cells to investigate whether the absorption of dipeptides by the peptide transporter PEPT1 alters the apical uptake of free cationic and neutral amino acids. Influx of L-[ ³H]Arg into Caco-2 cells was Na ⁺-independent and mediated mainly by the b ^0,+ system recognizing both cationic and neutral amino acids. Preincubation of cells with 10 mM of selected neutral, mono- or dicationic dipeptides increased the influx of L-Arg up to fourfold. Preloading with equivalent concentrations of the corresponding free amino acids also increased L-Arg influx but dipeptides always proved to be more efficient. The observed trans-stimulation was found to be specific for cationic amino acids since transport of L-[ ³H]Ala remained unaffected. We here demonstrate for the first time a direct interplay in amino acid and peptide transport in intestinal cells that may selectively alter the kinetics of amino acid absorption.