Molecular and cellular regulation of pancreatic duct cell function.
OBJECTIVE
The pancreatic duct epithelium is remarkable for its capacity to secrete HCO(3)(-) ions at concentrations as high as 140 mmol/l. The properties of the key transporters involved in this process and the central role played by cystic fibrosis transmembrane conductance regulator (CFTR) are the main focus of this review.


RESULTS
The Cl(-)/HCO(3)(-) exchanger at the apical membrane of pancreatic duct cells is now known to be SLC26A6. The 1: 2 stoichiometry and electrogenicity of this exchanger enable it to contribute to the secretion of HCO(3)(-) at high concentrations. The apical CFTR channels also appear to have sufficient HCO(3)(-) permeability to contribute directly to HCO(3)(-) secretion. There is a strong possibility that the Ca(2+)-activated Cl(-) channels at the apical membrane are members of the bestrophin family which, like CFTR, are also permeable to HCO(3)(-). More has been learned about the complex interactions between CFTR and other transporters within macromolecular complexes coordinated at the apical membrane by scaffolding proteins. Further details are also emerging of the protective paracrine roles of nucleotides, nucleosides, bile acids and trypsin in the regulation of ductal secretion.


CONCLUSIONS
Most of the key transporters involved in Cl(-) and HCO(3)(-) secretion have now been identified and characterized. Current research focuses on the molecular interactions between these transporters and the ways in which they are regulated by extracellular signals.
Steward
Martin C
MC
Faculty of Life Sciences, University of Manchester, Manchester, UK. martin.steward@manchester.ac.uk
Ishiguro
Hiroshi
H
D000075002:Bestrophins; D001639:Bicarbonates / Q000378:metabolism; D018118:Chloride Channels / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000378:metabolism*; D002713:Chlorine / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism; D010183:Pancreatic Ducts / Q000378:metabolism*; D015398:Signal Transduction
C113133:BEST1 protein, human; D000075002:Bestrophins; D001639:Bicarbonates; D018118:Chloride Channels; D027963:Chloride-Bicarbonate Antiporters; D005136:Eye Proteins; D026901:Membrane Transport Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002713:Chlorine