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

The majority of dietary amino acids are absorbed via the [H.sup.+]-di-/tripeptide transporter Pept1 of the small intestine. Proton influx via Pept1 requires maintenance of intracellular pH ([pH.sub.i]) to sustain the driving force for peptide absorption. The apical membrane [Na.sup.+]/[H.sup.+] exchanger Nhe3 plays a major role in minimizing epithelial acidification during [H.sup.+]-di-/tripeptide absorption. However, the contributions of HC[O.sup.-.sub.3]-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.sub.i] regulation during [H.sup.+]-peptide absorption. Using wild-type (WT) and Pat-1(-) mice, Ussing chambers were employed to measure the short-circuit current ([I.sub.SC]) associated with Pept1-mediated glycyl-sarcosine (Gly-Sar) absorption. Microfluorometry was used to measure [pH.sub.i] and [Cl.sup.-]/HC[O.sup.-.sub.3] exchange in the upper villous epithelium. In C[O.sub.2]/HC[O.sup.-.sub.3]-buffered Ringers, WT small intestine showed significant Gly-Sar-induced [I.sub.SC] and efficient [pH.sub.i] regulation during pharmacological inhibition of Nhe3 activity. In contrast, epithelial acidification and reduced [I.sub.SC] response to Gly-Sar exposure occurred during pharmacological inhibition of [Cl.sup.-]/HC[O.sup.-.sub.3] 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.sup.-]/HC[O.sup.-.sub.3] exchange in the presence of Gly-Sar revealed an increased rate of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] exchange that was both Pat-1 dependent and CA dependent. In conclusion, Pat-1 [Cl.sup.-]/HC[O.sup.-.sub.3] exchange contributes to [pH.sub.i] regulation in the villous epithelium during [H.sup.+]-dipeptide absorption, possibly by providing a HC[O.sup.-.sub.3] import pathway. acid-base transport; anion exchange; Pept1; carbonic anhydrase II; mouse doi:10.1152/ajpgi.00293.2009.