Organic secretion by striated ducts

In addition to their role in electrolyte homeostasis, striated ducts in the parotid and submandibular glands of many mammalian species engage in secre tion of organic products. This secretion usually is in the form of serous-l ike granules that lack substructure. Usually, the granules are in the 2.0-2 .5 mm range, but granules smaller than 0.1 mm and larger than 12 mm have be en observed. In mustelids, striated duct cells contain rhomboidal crystallo ids in their apical cytoplasm; in dogs and at least two bat species, the ap ical plasmalemma is festooned with perpendicularly-oriented rods. Rather th an granules, the supranuclear cytoplasm of duct cells in a number of specie s contains spherical or oblong vesicles. These may convey glycoproteins to the luminal surface where they are incorporated into the glycocalyx or the plasma membrane. Certain vesicles appear to be involved in the uptake of fo reign proteins introduced retrogradely into the main excretory duct or of a ltered proteins produced by acinar cells in streptozotocin-induced diabetes .