Figure 4. Steady‐state HCO₃ ⁻ fluxes in the perfused duct model at rest, and following cAMP stimulation and elevation of the luminal HCO₃ ⁻ concentration.

Steady‐state fluxes of HCO₃ ⁻ mediated by (clockwise from top left) NHE1, AE2, NBC1, SLC26A6 and CFTR. Fluxes correspond to the steady‐state values attained in Fig. 3. Results are shown for both the 1:2 Cl⁻:HCO₃ ⁻ stoichiometry of SLC26A6 (A) and for the 1:1 stoichiometry (B). In each case, the first panel represents the unstimulated duct perfused with the normal 25 mm HCO₃ ⁻ solution, the second panel shows the effect of altering the transporter activities to represent cAMP stimulation, and the third panel shows the effect of raising the luminal HCO₃ ⁻ concentration to 125 mm. Fluxes are given in nmol min⁻¹ cm⁻². Also shown are the steady‐state intracellular concentrations of Cl⁻ and HCO₃ ⁻ (mm) and the basolateral membrane potential. [Color figure can be viewed at wileyonlinelibrary.com]