Ultrastructure of the main excretory duct epithelia of the rat parotid and submandibular glands with a review of the literature.

The fine structure of the main excretory duct (MED) epithelia of the rat parotid and submandibular glands was investigated by scanning and transmission electron microscopy. The structure of these two MED epithelia was compared. Five principal cell types were observed in the MED epithelium of the parotid gland--cuboidal, basal, light (types I and II), dark, and tuft cells. The cuboidal cells, which were stratified in two or three layers, were the most numerous. Basal cells were situated adjacent to the basal lamina of the epithelium. The type I light cells had well-developed basal plasma membrane infoldings. The type II light cells had poorly developed basal plasma membrane infoldings. The dark and tuft cells resembled those of the MED epithelium of the rat submandibular gland. Four principal cell types were observed in the MED epithelium of the submandibular gland--light cells (types I and II), dark, tuft, and basal cells. The two types of light cells were the most numerous. Dark cells with regular and dense microvilli were relatively narrow in shape and had complicated basal plasma membrane infoldings. There were numerous vesicles or channel-like vesicles in their apical cytoplasm. Tuft cells were characterized by prominent microvilli, many vesicles of various sizes in the apical cytoplasm, and no basal infoldings. Peroxisomes were present in the MED epithelia of the rat parotid and submandibular glands, especially in light and cuboidal cells.