Figure 6. Extracellular chloride affects the I–V of prestin-transfected CHO cells.

Current–voltage (I–V) characteristics from A, an untransfected and B, a prestin-transfected CHO cell. A voltage ramp from −90 to +40 mV was used to generate the I–V curves and the zero current potential, V_R, was determined from the current curve intercept. The whole-cell recordings used [Cl⁻]_i= 11 mm in the pipette (see Methods). 25 mm HCO₃⁻ equilibrated with CO₂ was present throughout. C, V_R for untransfected cells. In 2 mm Cl_o, V_R=−24 ± 3 mV (n= 6) and in 146 mm Cl_o V_R=−45 ± 3 mV (n= 6). The dotted line shows the (Nernstian) prediction for a simple chloride electrode when the internal chloride, Cl_i= 11 mm. No further correction for leak currents has been carried out to align the experimental data with the theoretical predictions. D, V_R for prestin-transfected cells. In the whole-cell (wc) recording configuration and in 2 mm Cl_o, V_R=−75 ± 10 mV (n= 5); in 146 mm Cl_o, V_R=−51 ± 4 mV (n= 5). In the perforated patch (pp) configuration and in 2 mm Cl_o, V_R=−73 ± 8 mV (n= 7); in 146 mm Cl_o, V_R=−32 ± 8 mV (n= 7). The dotted line shows the theoretical prediction for V_R for an antiporter with a 1:2 Cl⁻:HCO₃⁻ stoichiometry derived from eqn (1) using [Cl⁻]_i= 11 mm and [HCO₃⁻]_i= 15 mm. A stoichiometry of 2:1 Cl:HCO₃ would result in a line with a negative slope, −58 mV per decade.