Mechanisms of bicarbonate secretion in the pancreatic duct
MC Steward, H Ishiguro, RM Case - Annu. Rev. Physiol., 2005 - annualreviews.org
MC Steward, H Ishiguro, RM Case
Annu. Rev. Physiol., 2005•annualreviews.org▪ Abstract 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 …
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 …
▪ Abstract
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 HCO3−-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.
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