Fig. 2. Apical redistribution of TfR does not result from diffusion across disrupted tight junctions. Transmission electron micrographs are shown of control cells (A) and cells pretreated for 15 minutes with 10 µM BFA (B,C) and then incubated basolaterally with 15 µg/ml HRP-Tf in the presence of absence of BFA for another 30 minutes. In all cases, the HRP reaction product is limited to endosomes and to the basolateral membrane (arrowheads), ending abruptly at the tight junction, with no product present at the apical plasma membrane (arrows). Scale bar, 1 µm (A,B); 0.5 µm (C).