Quantitation of Biosynthesis and Secretion of Mucin Using Metabolic Labeling

Most epithelial mucins are secretory glycoproteins. The mucin-producing cells are characterized by large intracellular stores of these very large and complex glycoproteins ( 1 , 2 ). These secretory mucins form mucous layers on the apical side of the cells, protecting the vulnerable epithelium, while allowing selective interactions with the apical environments, which is typically the lumen of an organ that is continuous with the outer world. Secretion from mucin-producing cells is regulated. Normally, mucins are constitutively secreted in relatively low amounts, which are sufficient under normal conditions to sustain the thickness of the mucous layer. On acute threats, the accumulated mucins may be secreted in bulk amounts to provide mucus as an effective, yet temporary, means of epithelial protection ( 1 , 2 ). Both types of secretion require synthesis of mucin: constitutive secretion demands a continuous low level of biosynthesis, whereas stimulated secretion requires massive synthesis to replenish the diminished resources. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.