Uptake of cationized ferritin by the epithelium of the main excretory ductof the rat submandibular gland

Previous studies demonstrated that the main excretory duct (MED) of the rat submandibular gland can internalize exogenous protein in addition to reabs orbing and secreting electrolytes. However, more precise studies have not b een conducted. The aim of this study was to elucidate the cell types respon sible for endocytosis of an exogenous protein (ferritin) and to follow the movements of the endocytosed protein in the ductal epithelial cells. The MEDs of the right submandibular gland of male Wistar rats were exposed near the glands proper and cationized ferritin solution was injected into e ach MED through a fine glass cannula. The MEDs were removed at intervals af ter ferritin injection, fixed and examined by transmission electron microsc opy. The epithelium of the MED of the rat submandibular gland was pseudostratifi ed and consisted of light (types I and II), dark, tuft and basal cells. Upt ake of ferritin by the light (types I and II) and dark cells occurred frequ ently. Small vesicles and multivesicular bodies containing ferritin particl es were observed in the supra-nuclear and lateral nuclear cytoplasm. Endocy tosis of tracers by tuft cells was rare. Some of the small vesicles and the multivesicular bodies were acid phosphatase-positive. By 60 min after trea tment, ferritin-containing small vesicles and multivesicular bodies appeare d in the basal cytoplasm. Ferritin particles were also observed in basal ex tracellular spaces. The light (types I and II), dark and tuft cells (latter rarely) participate d in endocytosis of exogenous proteins in the epithelium of the MED of the rat submandibular gland. Almost all of the internalized proteins appeared t o be processed by the lysosomal system, and some proteins were released int o the extracellular spaces. Anat Rec 258:108-113, 2000. (C) 2000 Wiley-Liss , Inc.