MUCINS IN AIRWAY SECRETIONS FROM HEALTHY AND CHRONIC BRONCHITIC SUBJECTS

Little is known about whether the properties of respiratory mucins are altered as a result of airway irritation, but histochemical studies o f respiratory tract secretory cells show a more 'acidic' staining patt ern after exposure to tobacco smoke. Furthermore it has been suggested that proteoglycans are the major glycoconjugates in 'normal' respirat ory secretions, whereas mucins predominate in sputum. To investigate t hese observations further, mucins from secretions collected from the t racheal surface of healthy non-smoking 'normal' subjects and sputum fr om patients with chronic bronchitis were compared. All samples contain ed one major mucin population after density-gradient centrifugation, a nd a small amount of 'denser' mucin was present in some chronic bronch itic and one of the 'normal' samples. Proteoglycans were not a major c omponent of 'normal' secretions. The major mucin population from chron ic bronchitic samples had molecular masses between 10 and 30 MDa and b ehaved as random coils in solution. Whole mucins from 'normal' individ uals and chronic bronchitic patients were excluded from Sepharose CL-2 B, whereas reduced subunits were included. Proteolysis of subunits yie lded two populations of high-molecular-mass glycopeptides differing in size, suggesting the presence of two different tandem repeat regions in the mucins. Finally, mucins from patients with chronic bronchitis a re less, rather than more, acidic than those from 'normal' individuals . Mucins from bronchitic sputum and 'normal' secretions are thus simil ar in their macromolecular properties, but differ slightly in charge d ensity.