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

Abstract

The majority of dietary amino acids are absorbed via the H+-di-/tripeptide transporter Pept1 of the small intestine. Proton influx via Pept1 requires maintenance of intracellular pH (pHi) 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 pHiregulation during H+-peptide absorption. Using wild-type (WT) and Pat-1(−) mice, Ussing chambers were employed to measure the short-circuit current ( Isc) associated with Pept1-mediated glycyl-sarcosine (Gly-Sar) absorption. Microfluorometry was used to measure pHiand Cl−/HCO3−exchange in the upper villous epithelium. In CO2/HCO3−-buffered Ringers, WT small intestine showed significant Gly-Sar-induced Iscand efficient pHiregulation during pharmacological inhibition of Nhe3 activity. In contrast, epithelial acidification and reduced Iscresponse 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 (CAII), 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−INexchange that was both Pat-1 dependent and CA dependent. In conclusion, Pat-1 Cl−/HCO3−exchange contributes to pHiregulation in the villous epithelium during H+-dipeptide absorption, possibly by providing a HCO3−import pathway.