Fig. 4.

In vivo function and in vitro transport activity of Ci-Slc26aα mutants. (A–E) Mosaic expression (red channel) of WT (A) and Ci-Slc26aα point mutants (B–E) in Ci-Slc26aαMO2–injected embryos. Green channel, fluorescein-tagged Ci-Slc26aαMO2C; bright channel, transilluminated images. The white arrowhead indicates the lumen, and the yellow arrowhead indicates a substantial reduction of lumen. (F) Representative whole-cell transport currents of WT and Ci-Slc26aα point mutants expressed in CHO cells. Divalent substrates (10 mM) were applied to the extracellular side, yielding electrical outward currents for functional transporters. Intracellular and extracellular Cl⁻ concentrations were 10 mM and 100 mM, respectively. Mutant R444C also shows transport in the absence of divalent anions and has an altered current–voltage relationship indicative of uncoupled Cl⁻ permeation as an additional transport mode (Fig. S7 D and E). (G) Summary of data obtained from experiments in F. Bars indicate currents on application of the substrate measured at 0 mV membrane potential and normalized to the cell surface (mean ± SEM).