[Keratin filaments in epithelial cells of the excretory ducts of rabbit submandibular glands--an immunohistochemical and ultraimmunohistochemical study].

To clarify the roles of various keratin proteins, the distributions of eight keratin intermediate filament proteins (keratins 7, 8, 10, 13, 14, 18, 19 and 20) in the epithelial cells of the excretory ducts of rabbit submandibular glands were studied immunohistochemically and ultraimmunohistochemically. The epithelia of excretory ducts were composed of columnar cells and basal cells. In the columnar cells, intermediate filaments formed a network at the apical area, that is, an apex network connected with desmosomes. Keratins 7, 18 and 20 were detected in the upper layer of the network and keratins 8, 18 and 20 in the lower layer. The intermediate filaments containing keratin 7 were also connected with hemidesmosomes on the basal side. Keratins 7, 18 and 20 were found throughout the entire cytoplasm of the columnar cells. Keratins 8 and 14 were expressed near the nucleus, forming a ring-like structure around the Golgi apparatus in the columnar cells. In the basal cells, by contrast, the intermediate filaments were concentrated around the nucleus, forming a juxtanuclear network which contained keratin 10. Keratin 13 was detected between the juxtanuclear network and the cell membrane, and was connected with both desmosomes and hemidesmosomes. Kratin 7 filaments were contained throughout the entire cytoplasm of the basal cells. These results suggested that different functional subsets of keratin filaments could be distinguished in the epithelial cells of the excretory ducts of the submandibular glands. In the columnar cells, keratins 7, 8, 18 and 20 play a role in cell-cell contact or cell-matrix contact, and both keratins 8 and 14 seem to be involved in the structure of the Golgi apparatus. In the basal cells, keratin 10 may serve to position and anchor the nucleus within the cell, and keratin 13 plays a role in cell-cell and cell-matrix contacts.