Tadanobu Ban

Fine-structural characteristics of the liver of the cod (Gadus morhua macrocephalus), with special regard to the concept of a hepatoskeletal system formed by Ito cells

SummaryThe liver of the adult cod (teleost, Gadus morhua macrocephalus) was observed with transmission and scanning electron microscopy. Hepatocytes of this animal are extremely large (about 50–70 μm in diameter) and characterized by numerous large lipid droplets (5–15 μm in diameter) showing fluorescence for vitamin A, though weaker than that of Ito cells. No Kupffer cells were recognized in the endothelial lining. Collagen fibrils are sparse in the perisinusoidal space, while Ito cells stretching their long cytoplasmic processes to the perisinusoidal as well as interparenchymatous spaces are frequent. There are a number of large desmosomes between the cytoplasmic processes, and all Ito cells seem to be interconnected by these junctions. The cytoplasm in the cell bodies and cell processes is occupied by bundles of intermediate filaments, while organelles are poorly developed. Small vesicles and caveolae are arranged along the plasma membrane. Scanning electron microscopy shows distinct three-dimensional networks consisting of Ito cells and their processes, which might be supporting elements of the liver tissue. We wish to emphasize the concept of this hepatoskeletal system.

Ultrastructural and immunocytochemical studies on the cytoskeleton in the anterior pituitary of rats, with special regard to the relationship between actin filaments and secretory granules*

SummaryAs previously reported, in anterior pituitary cells of the rat, secretory granules are linked with adjacent granules, cytoorganelles, microtubules, and plasma membrane by thin filaments, 4–10 nm in diameter. The quick-freeze, deep-etching method revealed that some of the filaments linking adjacent secretory granules show 5 nm-spaced striations on their surface which are known to be characteristic of actin. Immunocytochemistry showed that actin is localized in the cytoplasm beneath the plasma membrane, and around or between secretory granules. The heavy meromyosin decoration method demonstrated that actin filaments are mainly located in the cytoplasm beneath the plasma membrane, while some actin filaments are connected with the limiting membrane of the secretory granules. The actin filaments associated with the secretory granules are considered to be involved in the intracellular transport of the granules, while those localized in the peripheral cytoplasmic matrix might control the approach of the secretory granules to the plasma membrane and their release.

Immunocytochemical demonstration of caldesmon (a calmodulin-binding, F-actin-interacting protein) in smooth muscle fibers and absorptive epithelial cells in the small intestine of the rat

SummaryThe distribution of caldesmon (a calmodulin-binding, F-actin-interacting protein) (Sobue et al. 1982) and of actin was studied in the rats small intestine by means of light-microscopic immunocytochemistry. Positive immunostaining for caldesmon was seen in smooth muscle cells of the intestinal wall, and of blood vessels, and in the apical portion of the absorptive epithelial cells. The immunoreactivity in goblet cells was difficult to recognize. The positive reaction to immunostaining for actin showed almost the same pattern as that for caldesmon. These results suggest that this calmodulin-binding protein may play an important role in the control of actin-myosin interaction in smooth muscle cells and in non-muscle cells.

Immunocytochemical demonstration of caldesmon and actin in thyroid glands of rats.

SummaryThe distribution of caldesmon (a calmodulin-binding, F-actin interacting protein; Sobue et al. 1982) and actin was studied in the rat thyroid gland by means of light-microscopic immunocytochemistry, and the fine-structural distribution of actin filaments was examined by use of heavy meromyosin (HMM). Caldesmon and actin were demonstrated in the apical cytoplasm of almost all the follicle epithelial cells in normal as well as TSH-treated animals. Immunoreactivities for both caldesmon and actin showed almost the same pattern in localization. The smooth muscle cells of the blood vessels were also positive for caldesmon and actin. By electron microscopy, numerous actin filaments decorated by HMM and running perpendicularly or randomly to the apical surface were recognized in the apical cytoplasm of the follicle epithelial cell. These results suggest that caldesmon and actin, in conjugation with calmodulin, play a role in the regulation of cellular activity such as exocytosis and endocytosis in the apical portion of the follicle epithelial cell.