Fig 3. Cl^--HCO₃^- exchange activity.

Intracellular pH (pH_i) and membrane potential (V_m) changes of water injected Xenopus oocyte (A) and oocytes expressing Slc26a9 (B) or Slc26a7 (C) are measured using microelectrodes (see Methods). Bath Cl^- removal (0Cl^-, gluconate replacement) in the presence of 5% CO₂/ 33 mM HCO₃^- (pH 7.5) will increase pH_i as Cl^- moves out of the oocyte in exchange for HCO₃^- (moving into oocyte). Na⁺ removal (in CO₂/HCO₃^-) is an indication of Na⁺/HCO₃^- cotransporter activity (Na⁺ and HCO₃^- moving out of the oocyte together). 0Cl^- elicits a pHi increase (base loading) in Slc26a9 (B) cells but not Slc26a7 (C). 0Cl^- also elicits a Vm increase for both Slc26a9 and Slc26a7. Averaged pHi change rates (10-⁵ pH units/sec) and membrane potential changes (ΔmV) due to addition of CO₂/HCO₃^-, Cl^- removal, and Na⁺ removal are shown in D and E, respectively.