Electron micrographs of BHK antisense CHC cells incubated with a CTB-HRP conjugate. Electron micrographs of BHK antisense CHC cells incubated with a CTB-HRP conjugate. In A,B the non-induced control cells were incubated for 30 minutes at 0°C before fixation and processing for EM. The CT conjugate labeled the entire cell surface, including caveolae (A) and clathrin-coated pits (B). C,D show non-induced cells incubated with CTB-HRP for 30 minutes at 37°C, and both caveolae (C) and clathrin-coated pits (D) were labeled, whereas the rest of the cell surface appeared largely unlabeled. In E,F, the BHK cells were induced for antisense CHC expression before incubation with CTB-HRP for 30 minutes at 37°C. The toxin conjugate was distinctly present in caveolae (E) and in clathrin-coated pits (F), which were frequent (two to fivefold increase compared with non-induced control cells). Bar, 100 nm. Maria L. Torgersen et al. J Cell Sci 2001;114:3737-3747 © The Company of Biologists Limited 2001