Backround: 

Inhibition of the apical Na⁺/H⁺ exchanger isoform 3 (NHE3) interferes with dipeptide uptake in intestinal cell lines.

Aim: 

This study investigates the mode of coupling between electrolyte and nutrient transporters involved in H⁺-symport driven dipeptide uptake in native murine intestine.

Methods and Results: 

The luminal application of the dipeptide Gly-Sar resulted in a strong increase in murine small intestinal fluid absorption and a decrease in villous enterocyte pHi, measured by two-photon microscopy in vivo. It caused a strong short circuit current (Isc) response in chambered jejunal mucosa in vitro, and a decrease in pHi in BCECF-loaded enterocytes in isolated jejunal villi. Genetic ablation of PEPT1 abolished Gly- Sar-induced fluid absorption, Isc response, and enterocyte acidification. Genetic ablation of NHE3 did not change the distribution or amount of PEPT1 in the brush border membrane, but abolished Gly-Sar-induced fluid absorption, strongly diminished Isc response, but significantly enhanced enterocyte acidification in the absence but not the presence of CO₂/ HCO₃^- . Genetic ablation of the apical Cl^-/HCO₃^- exchanger Slc26a6 did not influence Gly-Sar-induced Isc, but significantly enhanced enterocyte acidification in the presence but not the absence of CO₂/HCO₃^-. The transmembrane Na⁺ was more important than the proton gradient to sustain high rates of H+/dipeptide transport in the native epithelium.

Conclusions: 

NHE3 and Slc26a6 are equally important for recovery of Gly- Sar-induced cellular acid loads, but only NHE3 is essential for H⁺/dipeptide transport. Via H⁺ recycling through NHE3, the transmembrane Na⁺ gradient energizes H⁺/dipeptide transport in the native epithelium even in the complete absence of a proton gradient.