Developmental changes in the ultrastructure and properties of secretory granules of the mucous cell found in the postnatal mouse parotid gland

Mucous cells were found in the terminal clusters and acini of the parotid gland in early postnatal mice. We examined the development of the parotid gland and histological changes in the properties of the secretory granules of the mucous cells using light and electron microscopy. No mucous cells were recognizable on the day of birth. The cells were observed one day after birth and increased gradually until the 5th day. The granules of the mucous cells showed an intensely positive reaction upon PA-Schiff and alcian blue staining and showed low electron density and a bipartite substructure with a central dense core and a rim of lower density. The central dense core increased gradually from the first day after birth and was entirely digestible with pronase. On and after the 7th day after birth, the mucous cells decreased gradually and disappeared ten days later.These findings suggest that many of the granules in the mucous cells change to serous granules, since mucous cells appear only within a limited period and that the granule cores contain protein and increase in size with development.