Aims: The intestinal di-/tripeptide transporter PEPT1 is believed to contribute significantly to the absorption of food-derived amino acids. In spite of the loss of this intestinal transporter, pept1^-/- mice (Deltagen) do not show any obvious phenotype. Here we investigated if there is a compensation by upregulation of the electrogenic amino acid transporters located in the apical membrane of jejunal enterocytes. Methods: Stripped jejunal epithelia from C57BL/6J wildtype (WT) and pept1^-/- (KO) mice were mounted in Ussing chambers, luminally perfused with solutions containing saturating (20 mM) concentrations of dipeptides, amino acids or glucose and the short circuit current (SCC) induced by these substrates was measured. Results: The glucose-induced current was similar in WT (88,9 mA/cm², n=31) and KO (108,9 mA/cm², n=21) and was used as a reference for the other substrates. Whereas the dipeptide glycilsarcosine induced SCC only in WT (39,3±10 mA/cm²,47 % of glucose-induced current), the currents induced by amino acids were not different in WT and KO (proline WT: 46,3±7,5 mA/cm²,52 % KO: 54,8±9 mA/cm²,49 %; glycine WT: 21,3±5,9 mA/cm²,30 % KO: 35,5±8 mA/cm²,32 %). Since lysine uptake occurs via the b0,+A/rBAT exchanger, in native epithelia maximal transport rate is determined by the availability of neutral amino acids on the cytosolic side. To overcome this limitation, the basolateral membrane of the enterocytes was permeabilized by saponin and glycine was added to the serosal side. This increased the lysine- induced current in both, WT and KO, but did not uncover significant differences between them. Conclusion: The results indicate that electrogenic amino acid transporters are not upregulated in the pept1^-/- mouse as compared to WT. This may suggest that their transport capacity is large enough to ensure nitrogen supply even if PEPT1 is missing. Thus, the significance of PEPT1 in WT remains unresolved.