Fig. 5.

SLC4A11 does not transport bicarbonate. HEK293 cells, grown on glass coverslips and transfected with cDNA encoding SLC4A11 or empty vector, were incubated with the pH-sensitive dye BCECF-AM. Coverslips were placed in a fluorescence cuvette and fluorescence was monitored in a fluorimeter, using λ_excitation = 440 and 502.5 nm and λ_emission = 528.7 nm. A: cuvette was perfused alternately with Cl⁻-containing (shaded bar) and Cl⁻-free (open bar) Ringer's buffers, bubbled with 5% CO₂. Black and gray traces represent results from cells transfected with SLC4A11 (n = 9) and vector (pcDNA3.1, n = 7), respectively. B: mean of Cl⁻/HCO₃⁻ exchange activity (J_H⁺) calculated from the initial rate of pH_i change during perfusion with Cl⁻-free buffer. C: sodium-dependent bicarbonate transport activity. BCECF-loaded HEK293 cells, transiently expressing SLC4A11 (black trace, n = 16) or empty vector (gray trace n = 12), were equilibrated in Na⁺-free Ringers buffer (gray bar), containing 5 μM ethyl-isopropyl amiloride (EIPA). All buffers in this experiment were bubbled with 5% CO₂. NH₄Cl was added (black bar) and then perfusion began with NH4Cl and Na⁺-free Ringers buffer (gray bar). Finally, cuvette was perfused with Na⁺-containing Ringer's buffer (white bar). D: Na⁺-dependent bicarbonate transport activity estimated by [H⁺] flux (J_H⁺), following switching to Na⁺-containing medium (Student's t-test; all comparisons not significant for SLC4A11 vs. control at each tested pH value).