Mechanisms of bicarbonate secretion in the pancreatic duct.
In many species the pancreatic duct epithelium secretes HCO3- ions at a concentration of around 140 mM by a mechanism that is only partially understood. We know that HCO3- uptake at the basolateral membrane is achieved by Na+-HCO3- cotransport and also by a H+-ATPase and Na+/H+ exchanger operating together with carbonic anhydrase. At the apical membrane, the secretion of moderate concentrations of HCO3- can be explained by the parallel activity of a Cl-/HCO3- exchanger and a Cl- conductance, either the cystic fibrosis transmembrane conductance regulator (CFTR) or a Ca2+-activated Cl- channel (CaCC). However, the sustained secretion of HCO3- into a HCO- -rich luminal fluid cannot be explained by conventional Cl-/HCO3- exchange. HCO3- efflux across the apical membrane is an electrogenic process that is facilitated by the depletion of intracellular Cl-, but it remains to be seen whether it is mediated predominantly by CFTR or by an electrogenic SLC26 anion exchanger.
Steward
Martin C
MC
Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom. martin.steward@man.ac.uk
Ishiguro
Hiroshi
H
Case
R Maynard
RM
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D006801:Humans; D010183:Pancreatic Ducts / Q000378:metabolism*
D001639:Bicarbonates