Figure 4. Lack of HCO3 - and Cl- conductances in a DF508 CF duct. In this experiment we tested the effect of cAMP + ATP on both CFTR HCO3 - and Cl- conductances. As shown, HCO3 - and Cl- gradients were established either from lumen to cell or vice versa while perfusing the contralateral side with the impermeant anion gluconate. Stimulating CFTR with cAMP + ATP had little effect on either HCO3 - or Cl- diffusion potentials and conductance suggesting that the HCO3 - and Clconductances in wild type (normal) and R117H /DF508 CF ducts are most likely due to activation of CFTR and not likely due to activation of any other Cl- conductance.