Effects of Slc26a6 deletion and CFTR inhibition on HCO3- secretion by mouse pancreatic duct

Pancreatic duct epithelium secretes HCO3--rich fluid, which is dependent on cystic fibrosis transmembrane conductance regulator (CFTR). HCO3- transport across the apical membrane is thought to be mediated by both SLC26A6 Cl--HCO3- exchange and CFTR HCO3- conductance. In this study we examined the relative contribution and interaction of SLC26A6 and CFTR in apical HCO3- transport. Interlobular pancreatic ducts were isolated from slc26a6 null mice. Intracellular pH (pHi) was measured by BCECF microfluorometry. Duct cells were stimulated with forskolin and alkalinized by acetate pre-pulse in the presence ofHCO3--CO2. Apical HCO3- secretion was estimated from the recovery rate of pHi from alkaline load. When the lumen was perfused with high-Cl- solution, the rate of apical HCO3- secretion was increased by luminal application of CFTRinh-172 in ducts from wild-type mice but it was decreased in ducts from slc26a6 -/- mice. This suggests that slc26a6 and CFTR compensate/compete with each other for apical HCO3- secretion with high Cl- in the lumen. With high HCO3- in the lumen, luminal CFTRinh-172 reduced the rate of apical HCO3- secretion in both wild-type and slc26a6 -/- ducts. This suggests that HCO3- conductance of CFTR mediates a significant portion of apical HCO3- secretion with high HCO3- in the lumen.