The uptake of cationized ferritin by guinea-pig gall bladder in vitro.

Tissue pieces of guinea-pig gall bladder were grown in vitro for up to ten days. Over this period at different intervals, specimens were exposed to cationized ferritin in culture medium for 1 h and then grown in ferritin free medium for up to 24 h. Other specimens were grown in culture medium containing cationized ferritin for up to 24 h. Both treatments produced a similar morphological sequence. Electron microscopy at all intervals studied showed the cationized ferritin was first bound by the apical cell membrane, clumped and internalized in large 400 nm vesicles. It was then carried to lysosomes in the region of the Golgi apparatus. Within 1 h, the marker was exocytosed in clumps into the lateral intercellular space, accumulating against the basement membrane in a roughly regular approximately 60 nm array. This pathway of cationized ferritin through the gall bladder epithelium is the same as that followed in vivo although the time taken was shorter in vitro.