Putative anion transporter-1 (Pat-1, Slc26a6) contributes to intracellular pH regulation during H+-dipeptide transport in duodenal villous epithelium.

The majority of dietary amino acids are absorbed via the H⁺-di-/tripeptide transporter Pepti of the small intestine. Proton influx via Pept1 requires maintenance of intracellular pH (pH_i) to sustain the driving force for peptide absorption. The apical membrane Na⁺/H⁺ exchanger Nhe3 plays a major role in minimizing epithelial acidification during H⁺-di-/tripeptide absorption. However, the contributions of HCO₃^--dependent transporters to this process have not been elucidated. In this study, we investigate the role of putative anion transporter-1 (Pat-1), an apical membrane anion exchanger, in epithelial pH, regulation during H⁺-peptide absorption. Using wild-type (WT) and Pat-1(-) mice, Ussing chambers were employed to measure the short-circuit current (I_sc) associated with Pept1-mediated glycyl-sarcosine (Gly-Sar) absorption. Microfluorometry was used to measure pH_i and Cl^-/HCO₃^- exchange in the upper villous epithelium. In CO₂/HCO₃^--buffered Ringers, WT small intestine showed significant Gly-Sar-induced I_sc and efficient pH_i regulation during pharmacological inhibition of Nhe3 activity. In contrast, epithelial acidification and reduced I_sc response to Gly-Sar exposure occurred during pharmacological inhibition of Cl^-/HCO₃^- exchange and in the Pat-1(-) intestine. Pat-1 interacts with carbonic anhydrase II (CAll), and studies using CAII(-) intestine or the pharmacological inhibitor methazolamide on WT intestine resulted in increased epithelial acidification during Gly-Sar exposure. Increased epithelial acidification during Gly-Sar exposure also occurred in WT intestine during inhibition of luminal extracellular CA activity. Measurement of Cl^-/HCO₃^- exchange in the presence of Gly-Sar revealed an increased rate of Cl^-_OUT/HCO₃^-_lN exchange that was both Pat-1 dependent and CA dependent. In conclusion, Pat-1 CI^-/HCO₃^- exchange contributes to pH_i regulation in the villous epithelium during H⁺-dipeptide absorption, possibly by providing a HCO₃^- import pathway. [ABSTRACT FROM AUTHOR]