Role of directional Ca2+ effect on reduced viscosities of mucus secretions from chicken trachea in vitro.

Reduced viscosities of fibrillar and gelatinous type mucins produced in response to high submucosal Ca2+ and low luminal Ca2+ effects were significantly higher than those of corresponding types of normal mucins. The increased reduced viscosity of experimental mucin samples was due to their aggregation with unique low molecular weight (mr 325,000 and 46,200) sulphate-rich components. The Ca2+ appeared to exert two opposing effects on viscosity properties of mucins; whereas Ca2+-dependent complexes between different types of mucins appeared to be a selective phenomenon between sulphate-rich mucins and components. Ester sulphate residue content rather than N-acetylneuraminic acid residue content of these mucins and low molecular weight components showed a very good correlation with their reduced viscosity and Ca2+-binding values.