Three-dimensional studies of the cytoskeleton of cultured hepatocytes: a quick-freezing and deep-etching study

The ultrastructure of the cytoskeleton of cultured mouse hepatocytes was studied by a quick-freezing and deep-etching method. Isolated mouse hepatocytes were cultured on collagen gels for 48 h, fixed in paraformaldehyde and centrifuged to prepare cell pellets. The hepatocytes were split open to remove cytoplasmic soluble proteins for replica preparations. Some specimens were decorated with anti-actin antibody or S1 myosin fragments to identify actin filaments. They were quickly frozen in isopentane-propane mixture, fractured in liquid nitrogen, deeply etched in a freeze-fracture machine and rotary shadowed by platinum and carbon. The basal cell membranes of hepatocytes were in contact with the collagen gels and the apical surface faced the culture medium. Networks of actin filaments were attached to the apical cell membranes, but intermediate filaments were localized along the basal layer. Some intermediate filaments were associated with cell organelles, such as the endoplasmic reticulum. The Golgi apparatus was less associated with the cytoskeleton and showed synthesized materials in the cisternae. Cytoskeletal organization in cultured hepatocytes was revealed three-dimensionally, indicating that the interaction of cell membranes with collagen gels is important for the organization of the cytoskeleton.