Gastrointestinal mucus gel rheology.

Mucus secretions from human and pig stomach; pig duodenum and pig colon have the same viscoelastic gel structure, as determined by mechanical spectroscopy. These mucus gels are readily solubilised by proteolysis or reduction with thiol agents but are stable with an unchanged mechanical spectra following exposure to pH 1-8, bile, bile salts and hypertonic 2 M NaCl. Gels of the same mechanical spectra and stability are reproduced by concentration of the isolated mucins purified free of protein, DNA and lipid (less than 1%). A direct correlation is observed between percentage of total mucin in polymeric form in the mucus secretion and its gel quality. The mechanical spectra of proteolytically digested mucus, together with the resistance of mucus to denaturing agents suggest carbohydrate-carbohydrate interactions are involved in gel matrix formation. Pig submaxillary mucin forms model gels with the same viscoelastic gel structure as other gastrointestinal gels. Wide variations in the composition and length of the carbohydrate chains of mucins do not affect the gel-forming properties.