Downregulated in adenoma and putative anion transporter  are regulated by CFTR in cultured pancreatic duct cells

The mechanism of the pancreatic ductal HCO[Formula: see text] secretion defect in cystic fibrosis (CF) is not well defined. However, a lack of apical Cl−/HCO[Formula: see text] exchange may exist in CF. To test this hypothesis, we examined the expression of Cl−/HCO[Formula: see text] exchangers in cultured pancreatic duct epithelial cells with physiological features prototypical of CF [CFPAC-1 cells lacking a functional CF transmembrane conductance regulator (CFTR)] or normal duct cells (CFPAC-1 cells transfected with functional wild-type CFTR, CFPAC-WT). Cl−/HCO[Formula: see text] exchange activity, assayed with the pH-sensitive dye 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein in cells grown on coverslips, increased about twofold in cells transfected with functional CFTR. This correlated with increased apical 36Cl influx in cells expressing functional CFTR and grown on permeable support. Northern hybridizations indicated the induction of downregulated in adenoma (DRA) in cells expressing functional CFTR. The expression of putative anion transporter PAT1 also increased significantly in cells expressing functional CFTR. DRA was detected at high levels in native mouse pancreas by Northern hybridization and localized to the apical domain of the duct cells by immunohistochemical studies. In conclusion, CFTR upregulates DRA and PAT1 expression in cultured pancreatic duct cells. We propose that the pancreatic HCO[Formula: see text] secretion defect in CF patients is partly due to the downregulation of apical Cl−/HCO[Formula: see text] exchange activity mediated by DRA (and possibly PAT1).

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CFTR drives Na+- n HCO 3 − cotransport in pancreatic duct cells: a basis for defective HCO 3 − secretion in CF

AJP Cell Physiology ◽

10.1152/ajpcell.1999.276.1.c16 ◽

1999 ◽

Vol 276 (1) ◽

pp. C16-C25 ◽

Cited By ~ 94

Author(s):

Holli Shumaker ◽

Hassane Amlal ◽

Raymond Frizzell ◽

Charles D. Ulrich ◽

Manoocher Soleimani

Keyword(s):

Pancreatic Duct ◽

Basolateral Membrane ◽

Molecular Evidence ◽

Transmembrane Conductance Regulator ◽

Transmembrane Conductance ◽

Duct Cells ◽

Pancreatic Duct Cells ◽

Pancreatic Dysfunction ◽

Cf Transmembrane Conductance Regulator ◽

Normal Duct

Pancreatic dysfunction in patients with cystic fibrosis (CF) is felt to result primarily from impairment of ductal[Formula: see text] secretion. We provide molecular evidence for the expression of NBC-1, an electrogenic Na+-[Formula: see text]cotransporter (NBC) in cultured human pancreatic duct cells exhibiting physiological features prototypical of CF duct fragments (CFPAC-1 cells) or normal duct fragments [CAPAN-1 cells and CFPAC-1 cells transfected with wild-type CF transmembrane conductance regulator (CFTR)]. We further demonstrate that 1)[Formula: see text] uptake across the basolateral membranes of pancreatic duct cells is mediated via NBC and 2) cAMP potentiates NBC activity through activation of CFTR-mediated Cl− secretion. We propose that the defect in agonist-stimulated ductal[Formula: see text] secretion in patients with CF is predominantly due to decreased NBC-driven[Formula: see text] entry at the basolateral membrane, secondary to the lack of sufficient electrogenic driving force in the absence of functional CFTR.

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CFTR Functions as a Bicarbonate Channel in Pancreatic Duct Cells

The Journal of General Physiology ◽

10.1085/jgp.200810122 ◽

2009 ◽

Vol 133 (3) ◽

pp. 315-326 ◽

Cited By ~ 74

Author(s):

Hiroshi Ishiguro ◽

Martin C. Steward ◽

Satoru Naruse ◽

Shigeru B.H. Ko ◽

Hidemi Goto ◽

...

Keyword(s):

Cystic Fibrosis ◽

Membrane Potential ◽

Guinea Pig ◽

Pancreatic Duct ◽

Apical Membrane ◽

Transmembrane Conductance Regulator ◽

Duct Cells ◽

Pancreatic Duct Cells ◽

K Concentration ◽

Significant Pathway

Pancreatic duct epithelium secretes a HCO3−-rich fluid by a mechanism dependent on cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. However, the exact role of CFTR remains unclear. One possibility is that the HCO3− permeability of CFTR provides a pathway for apical HCO3− efflux during maximal secretion. We have therefore attempted to measure electrodiffusive fluxes of HCO3− induced by changes in membrane potential across the apical membrane of interlobular ducts isolated from the guinea pig pancreas. This was done by recording the changes in intracellular pH (pHi) that occurred in luminally perfused ducts when membrane potential was altered by manipulation of bath K+ concentration. Apical HCO3− fluxes activated by cyclic AMP were independent of Cl− and luminal Na+, and substantially inhibited by the CFTR blocker, CFTRinh-172. Furthermore, comparable HCO3− fluxes observed in ducts isolated from wild-type mice were absent in ducts from cystic fibrosis (ΔF) mice. To estimate the HCO3− permeability of the apical membrane under physiological conditions, guinea pig ducts were luminally perfused with a solution containing 125 mM HCO3− and 24 mM Cl− in the presence of 5% CO2. From the changes in pHi, membrane potential, and buffering capacity, the flux and electrochemical gradient of HCO3− across the apical membrane were determined and used to calculate the HCO3− permeability. Our estimate of ∼0.1 µm sec−1 for the apical HCO3− permeability of guinea pig duct cells under these conditions is close to the value required to account for observed rates of HCO3− secretion. This suggests that CFTR functions as a HCO3− channel in pancreatic duct cells, and that it provides a significant pathway for HCO3− transport across the apical membrane.

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