Ultrastructure of intracellular membranous system and intracellular transport of asialoglycoproteins in rat hepatocytes.

The ultrastructure of the intracellular membranous system in rat hepatocytes was observed three dimensionally with a scanning electron microscope using the aldehyde prefix osmium-dimethyl sulfoxide-osmium method. Intracellular organelles were clearly observed in three dimensions, and direct connection of tubular structures with the bile canalicular membrane was clearly seen. The transcellular pathway of asialoglycoproteins in isolated cultured rat hepatocytes was also investigated, by affinity cytochemistry, using gold-conjugated asialofetuin, under a transmission electron microscope. Gold particles were clearly seen not only in vesicles, endosomes and lysosomes, but also in the tubular structures. These results suggest that the tubular structures in rat hepatocytes directly participate in the transcellular transport of macromolecules. In addition, the frequent connections of tubular structures with the bile canalicular membrane indicate that these structures around the bile canaliculus may supply membrane components to the bile canalicular membrane.