Figure 3.

Effect of the membrane potential on HCO₃ ⁻ transport by slc26a3. The protocol shown in Fig. 2 C was used to measure changes in pH_i except that the changes in pH_i at each Cl_o ⁻ concentration were measured while holding the membrane potential alternately at −30, −100, and 40 mV. The membrane potential was clamped after the stabilization of Cl_i ⁻ and for 30 s before and during the duration of the subsequent measurement of Cl⁻/HCO₃ ⁻ exchange. No more that three Cl⁻ concentrations were tested in each oocyte to minimize error caused by the deterioration of the signal. (A) Example traces from the same oocyte exposed to 7.5 and 25 mM Cl_o ⁻ while holding the membrane potential at −30 (black traces), −100 (green traces), or 40 mV (red traces). Results from at least three measurements at each Cl⁻ concentration and at the indicated membrane potentials, similar to those in Fig. 3 A, are plotted in B and show the Cl_o ⁻-dependence of HCO₃ ⁻ transport at −30 (squares), −100 (circles), and 40 mV (triangles). Error bars represent SEM.