Ultrastructural and carbohydrate histochemical studies on the differentiation and renewal of mucous cells in the rat gastric fundus.

Gastric surface mucous cells (SMC), mucous neck cells (MNC) and their undifferentiated and immature precursors were studied by light and electron microscopic histochemistry. The secretory granules of SMC were smaller, more electron dense and more reactive to PAS and its analogues than those of MNC. Alcian blue demonstrated that the mucus of SMC was acidic and that of MNC was neutral. The periodic acid-thiocarbohydrazide-silver proteinate method revealed the pressence of carbohydrates in the golgi apparatus, condensing vacuoles, secretory granules, apical vesicles and tubules and cell coat. Maturation of SMC during their migration towards the free surface was reflected by an increase in size and number of secretory granules, an increase of RER and microfilaments, and a decrease of microvilli and apical vesicles and tubules. The secretory granules of older SMC were less acidic and possessed a proteinaceous core. Most MNC were fully differentiated, but some immature MNC containing only a few granules were found. Furthermore, undifferentiated cells and intermediates between SMC and MNC were also observed. The presence of both transitional and intermediate forms indicates that both SMC, and MNC arise from the same population of undifferentiated cells. Incorporation of 3H-thymidine revealed that undifferentiated cells, use isthmic SMC, MNC and intermediate cells are proliferative. No proliferative activity was found in foveolar SMC, parietal, chief, fibrillovesicular or endocrine cells.