Fig. 8. Effect of neutral and polar side-chain Q267 substitutions on NIS expression. Non-transfected COS-7 cells (NT) or COS-7 cells transfected either with WT rNIS, rQ267A or rQ267N NIS were assayed for I^- transport activity at 20 (A) or 160 (B) µM I^-. Assays were performed in the presence of 20 µM or 160 µM I^-/140 mM Na⁺ (colored bars) or 20 µM or 160 µM I^-/140 mM Na⁺ plus 80 µM perchlorate (white bars). Results are expressed in percentages with respect to WT NIS activity. y-Axis has been split into two scales. (C) Immunoblot. (D) Surface biotinylation. (E) Immunofluorescence analysis. All procedures were performed as described in Figs 3, 5 and 6, and in Materials and Methods.