Comparative studies of mucus and mucin physicochemistry

The transport of mucus on a ciliated epithelium, and the penetration of sperm through cervical mucus, have been shown to be functions of the rheological, principally viscoelastic, properties of the secretion. These physicochemical properties, in turn, are largely determined by the composition and concentration of mucin glycoproteins, which are the principal macromolecular components of the secretion. These functions and properties of various types of mucous secretions are discussed, emphasizing both similarities and differences. Background and data are presented supporting these concepts, based on studies of human cervical and middle ear mucus, as well as bovine cervical and canine tracheal mucus. A major determinant of differences in function between mucus samples appears to be the carbohydrate composition of the mucin, after corrections are made for environmental factors such as pH, ionic strength and mucin concentration Mucin behaviour also depends on specific solutes in the secretion, such as Ca2+. Although significant differences in mucus properties and function exist, it is hypothesized that these developed as variations of the major function common to all mucous secretions, which is to maintain and control the water balance of epithelial mucosa.