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 HCO 3- 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-/2HCO 3- 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.
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