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

摘要

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 pHi regulation 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 pHi and Cl-/HCO3- exchange in the upper villous epithelium. In CO2/HCO3--buffered Ringers, WT small intestine showed significant Gly-Sar-induced Isc and efficient pHi regulation during pharmacological inhibition of Nhe3 activity. In contrast, epithelial acidification and reduced Isc 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 (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-IN exchange that was both Pat-1 dependent and CA dependent. In conclusion, Pat-1 Cl -/HCO3- exchange contributes to pHi regulation in the villous epithelium during H+-dipeptide absorption, possibly by providing a HCO3- import pathway.