• Proton-coupled transport;
  • dipeptide;
  • intestine;
  • epithelium;
  • Caco-2 cells;
  • cell culture;
  • cephalosporin;
  • intracellular pH
  • 1
    pH-dependent transepithelial transport and intracellular accumulation of the hydrolysis-resistant dipeptide glycylsarcosine (Gly-Sar) have been demonstrated in the model human intestinal epithelial cell line, Caco-2.
  • 2
    Experiments with BCECF (2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein)-loaded Caco-2 cells demonstrated that dipeptide (Gly-Sar) transport across the apical membrane is coupled to proton flow into the cell.
  • 3
    A range of postulated substrates for the intestinal di/tripeptide carrier were tested for their abilities to: (a) inhibit pH-dependent [14C]Gly-Sar apical-to-basal transport and intracellular accumulation and (b) stimulate H+ flow across the apical surface of BCECF-loaded Caco-2 cell monolayers.
  • 4
    A range of compounds (including Gly-Gly, Leu-Leu, Gly-Gly-Gly, cefadroxil and cephalexin) caused marked acidification of intracellular pH when perfused at the apical surface of Caco-2 cell monolayers. In contrast leucine and D-Leu-D-Leu failed to induce proton flow. The ability to induce proton-flow across the apical surface by these compounds, in this intestinal epithelium, was directly correlated to the relative inhibitory effects on [14C]-Gly-Sar transport and accumulation.
  • 5
    The determination of substrate-induced intracellular pH change in the Caco-2 cell system may provide a useful rapid screen for candidate substrates for absorption via H+-coupled transport mechanisms such as the intestinal di/tripeptide carrier in an appropriate physiological context.