Fig. 6. Polarised MDCKI cells expressing kAE1 are permeable to biotin reagent. MDCKI (A), MDCKI-kAE1(R901Stop) (B) and MDCKI-kAE1 (C) cells were selectively biotinylated on the apical surface. Biotinylated proteins were detected using a FITC-conjugated anti-biotin antibody. (D) MDCKI-kAE1 cells stained for biotinylated proteins (green, top panel) and kAE1 (red, middle panel). kAE1 cells have lateral staining (C, top panel D) suggesting that they are permeable to the usually impermeant biotinylation reagent. Polarised MDCKI-kAE1 cells biotinylated on the lateral membranes (green) clearly correspond to cells expressing kAE1 (red) (D, bottom panel). Scale bar, 15 µm