Ultrastructure of the "separating zone" of rat submandibular gland striated duct cells.

The separating zone of rat submandibular gland striated duct cells were studied in detail by electron microscopy. In order to get optimal stimulation of the glands the animals were starved for 24 h followed by feeding 15 min before sacrifice, and tissue removal. The separating zone is morphologically defined by numerous filaments which are located within the apical part of cell. Some of the filaments had a parallel arrangement, running horizontally and being attached to belt desmosomes at the cell periphery. Following the shedding of apical blebs, these filaments appeared to constitute the luminal boundary of striated duct cells. It was observed that the separating zones showed different degrees of density. This is supposed to reflect different stages in the reconstruction of the apical cell surface. It is thus considered that the separating zone, with numerous filaments, is of importance both of the apical secretion per se, and the formation of the new apical cell membrane.