Bronchial Secretions and Mucociliary Clearance

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Abstract
Impaired mucociliary clearance of inhaled aerosols may be due, in part, to abnormal consistency of the bronchial secretions, as indicated by experiments in animals with mucolytic agents; however, changes in the consistency of the secretions are difficult to correlate with changes in the overall composition. Evidence suggests that the basic gel structure of the bronchial secretions consists of long glycoprotein molecules crosslinked by disulfide bonds to form a loose network, whose elements are additionally cross-linked to one another and to water molecules by hydrogen bonding to form a semisolid gel. The abnormally high coherence and viscosity of dense mucopurulent sputum is accompanied by increase in disulfide bond cross-linking, deoxyribose nucleoprotein fibril material, and some more stable cross-linking, possibly involving transpeptidation. We have found that sputum contains a γ-glutamy transpeptidase but this enzyme differs from those known to be involved in cross-linking.