Fig. 6.

Estimation of the HCO₃ ^– permeability of the apical membrane. (A) The lumen was microperfused, and cells were loaded with BCECF, pH-sensitive dye. A small region of the duct epithelium was selected for measurements of intracellular pH (pH_i). (B) Since the pancreatic duct is a leaky epithelium (transepithelial potential is small), the potential difference of the apical membrane (V_a) could be manipulated by changing the bath K⁺ concentration. HCO₃ ^– flux across the basolateral membrane was inhibited by the anion transport inhibitor, H₂DIDS (dihydro-4,4’-diisothiocyanatostilbene-2,2’-disulphonic acid). Voltage-driven fluxes of HCO₃ ^– across the apical membrane were detected as changes in pH_i. (C) Changes in pH_i resulting from changes in V_a. Theoretical curves based on 3 alternative apical HCO₃ ^– permeability values were superimposed on averaged data (mean ± SEM). (D) HCO₃ ^– fluxes across the apical membrane were abolished in pancreatic ducts isolated from a cystic fibrosis mouse model (∆F mouse) lacking in CFTR activity. Adapted from reference 27.