Fig. 4. Effect of BFA on milk protein secretion in MECs. Acini were incubated in the absence or presence of 5 µM BFA for 60 minutes at 37°C, cytospun, fixed, permeabilised with Triton X-100 and treated for immunofluorescence. (A) In control acinus (CO) numerous secretory vesicles labelled with the RAM/MSP antibody are detectable in the cytoplasm (arrows). In the presence of BFA, cytoplasmic secretory vesicles decorated with the antibody RAM/MSP were no more detectable. It is notable that in BFA-treated cells huge lipid globules, whose periphery is strongly labelled with RAM/MSP antibody, accumulate at the apical region (arrowheads) (BM, basal membrane; L, lumen). Bar, 10 µm. (B) Media from control and treated acini were analysed by immunoblotting to reveal the presence of milk proteins. In the control medium (lane -) immunoreactive bands correspond to the numerous milk proteins. The number of milk proteins found in the medium was drastically reduced in the presence of BFA (lane +).