A granular cell at the acinar-intercalated duct junction of the rat submandibular gland

A granular cell was present at the acinar-intercalated duct junction in submandibular gland of adult rats of several different strains. It occurred more frequently in females thanin males. It was a small pyramidalshaped cell, usually forming the most proximal part of the intralobular duct system. The cell contained a relatively large, basally located nucleus. Numerous heterogeneous granules, usually exhibiting both electron-dense and electron-lucent regions, were present in the apical cytoplasm. Exocytosis of the granules at the apical cell surface was occasionally seen. Dilated cisternae of endoplasmic reticulum were frequently observed between the apical granules and in the basal and lateral cytoplasm. The function of the granular cell is unknown. Their structure and location suggest that they may (1) constitute a mature secretory cell population, or (2) represent progenitor cells for acinar and/or intercalated duct cells.