Mechanisms of Hco3 Secretion by Pancreatic Duct

Pancreatic duct cells secrete a HCO3-rich ( 140 mM) fluid. Using a computer model of the pancreatic duct, Sohma, et al. have demonstrated that the activity of a Cl/ HCO3 exchanger with a 1 : 1 stoichiometry at the apical membrane would have to be suppressed in order to achieve such a HCO3-rich secretion. Recently the apical exchanger in pancreatic ducts has been identified as SLC26A6 and this probably mediates most of Cl-dependent HCO3 secretion across the apical membrane. SLC26A6 is reported to mediate electrogenic Cl/2HCO3 exchange when expressed in Xenopus oocytes. To assess the implications of this 1 : 2 stoichiometry for HCO3 secretion, we have reconstructed the Sohma model using MATLAB/Simulink. To do this we have formulated an expression for the turnover rate of Cl/2HCO3 exchange using network thermodynamics and we have estimated the constants from published experimental data. Preliminary data suggest that the 1 : 2 stoichiometry of SLC26A6 would favor HCO3 secretion at higher concentrations. J. Med. Invest. 56 Suppl. : 325-328, December, 2009