Inhibition of the putative anion transporter (PAT‐1, Slc26a6) impairs the ability of villous epithelial cells to regulate intracellular pH (pH i ) during peptide transport

The upper villus is exposed to acid challenge from H + influx via the H + dipeptide cotransporter PEPT1. Intracellular carbonic anhydrase activity facilitates diffusive H + movement to help maintain a transmembrane ion gradient allowing for maximal absorption through PEPT1. Other studies have revealed that carbonic anhydrase II (CAII) can interact with the apical membrane Cl − /HCO 3 − exchanger PAT‐1. Therefore, we hypothesized that CAII functions with PAT‐1, the predominant Cl − /HCO 3 − exchanger of the upper duodenal villus, to form a HCO 3 − transport metabolon at the apical membrane to regulate pH i during PEPT1 transport activity. Measurements of pH i by BCECF microfluoroscopy were conducted in wild‐type (WT) and PAT‐1 knockout (KO) upper duodenal villous epithelium exposed to the dipeptide glycyl‐sarcosine (gly‐sar) in Kreb's HCO 3 − Ringers. During gly‐sar exposure, inhibition of luminal Cl − /HCO 3 − exchange in WT epithelium with niflumic acid resulted in greater acid influx (NFA = −0.83 ± 0.94; control = −7.05± 0.89 mM/min, n = 3; p<0.05). Furthermore, a greater acid influx was observed in the PAT‐1 KO as compared to WT during gly‐sar exposure (−0.07 ± 0.79 vs. −9.54 ± 3.40 mM/min, n = 3, p<0.05). These observations suggest that PAT‐1 provides protection against intracellular acidification in the upper villous epithelium, perhaps by operating in reverse mode as a base‐loading mechanism for the cell. Supported by NIH.