Submitted on December 15, 2008
Revised on March 25, 2009
Accepted on March 27, 2009
Functional coupling of apical Cl-/HCO3- exchange with CFTR in stimulated HCO3- secretion by guinea pig interlobular pancreatic duct
Andrew K Stewart1, Akiko Yamamoto, M Nakakuki2, T Kondo2, Seth L. Alper1, and Hiroshi Ishiguro3*
1 Beth Israel Deaconess Med Ctr
2 Nagoya University Graduate School of Medicine
3 Nagoya University
* To whom correspondence should be addressed. E-mail: ishiguro{at}htc.nagoya-u.ac.jp.
Pancreatic ductal epithelium produces a HCO3--rich fluid. HCO3- transport across ductal apical membranes has been proposed to be mediated by both SLC26-mediated Cl-/HCO3- exchange and CFTR-mediated HCO3- conductance, with proportional contributions determined in part by axial changes in gene expression and luminal anion composition. In this study we investigated the characteristics of apical Cl-/HCO3- exchange and its functional interaction with Cftr activity in isolated interlobular ducts of guinea pig pancreas. BCECF-loaded epithelial cells of luminally-microperfused ducts were alkalinized by acetate pre-pulse or by luminal Cl- removal in the presence of HCO3--CO2. Intracellular pH recovery upon luminal Cl- restoration (nominal Cl-/HCO3- exchange) in cAMP-stimulated ducts was largely inhibited by luminal H2DIDS, accelerated by luminal CFTRinh-172, and was insensitive to elevated bath [K+]. Luminal introduction of CFTRinh-172 into sealed duct lumens containing BCECF-dextran in HCO3--free Cl--rich solution enhanced cAMP-stimulated HCO3- secretion, as calculated from changes in luminal pH and volume. Luminal Cl- removal produced, after a transient small depolarization, sustained cell hyperpolarization of ~15 mV consistent with electrogenic Cl-/HCO3- exchange. The hyperpolarization was inhibited by H2DIDS and potentiated by CFTRinh-172. Interlobular ducts expressed mRNAs encoding CFTR, Slc26a6, and Slc26a3, as detected by RT-PCR. Thus, Cl--dependent apical HCO3- secretion in pancreatic duct is mediated predominantly by an Slc26a6-like Cl-/HCO3- exchanger and is accelerated by inhibition of CFTR. This study demonstrates functional coupling between Cftr and Slc26a6-like Cl-/HCO3- exchange activity in apical membrane of guinea pig pancreatic interlobular duct.
