Complex carbohydrates of rat tracheobronchial surface epithelium visualized ultrastructurally

Abstract

Application of cytochemical methods for complex carbohydrates at the light and electron microscopic levels served further to differentiate secretory cells of the rat tracheobronchial surface epithelium into serous and mucous categories, and permitted subclassification of serous cells into four types and of mucous cells into three types. The granules in different serous cells and Clara cells varied in staining with the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method, but generally lacked dialyzed iron (DI) affinity and apparently contained neutral glycoprotein. However, in some focal areas, serous and Clara cell granules showed a pattern of DI staining similar to the PA-TCH-SP reactivity. The PA-TCH-SP and DI methods stained granule glycoconjugate comparably in the three mucous cell types. The lack of high iron diamine (HID) affinity in these sites testified to carboxylated, periodate-reactive mucosubstance, presumably sialylated glycoprotein. The luminal surface of the apical plasmalemma of all surface epithelial cells stained with DI but lacked HID affinity. The PA-TCH-SP technique stained the surface of the apical plasmalemma of mucous cells, serous cells, and Clara cells in decreasing order of intensity. Microvilli of ciliated cells were PA-TCH-SP-positive, but cilia were unreactive and apparently contained a glycosaminoglycan rather than the presumed sialylated glycoprotein of the other surfaces. DI and PA-TCH-SP reactivity of the apical far exceeded that of the basolateral plasmalemma in all surface epithelial cells. Two strata, presumed to be the lamina lucida and the lamina diffusa of the basement membrane under all the surface epithelial cells, stained with the DI but not the PA-TCH-SP method and apparently contained glycosaminoglycan. Intraepithelial cells, interpreted as globule leukocytes, appeared to represent mast cells infiltrating the epithelium and carrying out endocytic activity.