HEK 293 cells transiently transfected with SLC26A9 exhibit constitutive chloride currents under whole cell voltage clamp. (A) Cells transfected with GFP ± SLC26A9 were voltage clamped at −40 mV. A subset of cells were stimulated with 10 µM forskolin. SLC26A9-expressing cells exhibited constitutive chloride currents that were not enhanced by forskolin stimulation. Cells expressing GFP alone exhibited no significant basal current or response to forskolin. Representative tracings from at least three experiments each are shown. (B) SLC26A9-transfected cells exhibited linear I-V relations before, during, and after forskolin treatment. I-V curves are for the trace shown in A, labeled SLC26A9 + GFP + fsk, recorded at the indicated times (solid diamonds). HEK 293 cells transfected with GFP alone had negligible currents that did not contribute significantly to the I-V relations of SLC26A9-expressing cells (Supplemental text). All current values are normalized by cell capacitance.