FIGURE 4.

Activation of Slc26a2-mediated SO₄²⁻_i/OH⁻_o exchange by Cl⁻_o. A, example traces of Cl⁻_i (black) and pH_i (gray) in oocytes expressing Slc26a2. SO₄²⁻_iflux was terminated by removal of SO₄²⁻_o (period bordered by dashed line). SO₄²⁻ efflux did not start until the addition of 1 mm Cl⁻_o (period bordered by gray square), which triggered robust SO₄²⁻_i/OH⁻_o exchange with minimal SO₄²⁻_i/Cl⁻_o exchange. B, the relative rate of SO₄²⁻_i/OH⁻_o exchange is plotted as a function of the activating Cl⁻_o. The rates at each Cl⁻_o were normalized to the rate measured at 110 mm Cl⁻_o, which was taken as 100%. The plot is the average of 3–5 experiments and fitted to the Hill equation. C, the protocol in A was used to measure activation of SO₄²⁻_i/OH⁻_o exchange by 1 mm of the indicated anions (period marked by gray square). The results are mean ± S.E. of the number of experiments indicated in the columns.