Reflex mucus secretion in the airways serves a defense function that includes the binding of bacteria to mucus glycoconjugates thereby preventing bacterial adherence to the epithelium. We therefore compared the lectin- detectable glycoconjugate profile of the epithelial glycocalyx and luminal secretions under baseline conditions and after muscarinic receptor stimulation in the sheep trachea. The sheep were intubated with a double- balloon nasotracheal tube to create a tracheal chamber for collection of secretions. After an initial lavage of the chamber to clear it of secretions, the sheep received an intravenous injection of normal saline, 0.5 mg/kg pilocarpine, or 0.5 mg/kg pilocarpine after pretreatment with 0.2 mg/kg atropine. Tracheal lavage was repeated 2 h later, and the sheep were then killed. An enzyme-linked lectin assay and lectin histochemistry were used to characterize glycoconjugate residues in tracheal secretions and in the apical epithelial glycocalyx, respectively. Eight different lectins were used to detect N-acetyl galactosamine, α-galactose, α-galactose-N-acetyl galactosamine, β-galactose, β-galactose-N-acetyl galactosamine, α-fucose, α-glucose, α-mannose and α-(2-3)sialyl residues. After normal saline, reactivity was present for all glycoconjugates in secretions and in the glycocalyx. After pilocarpine, there was a greater reactivity for α- galactose, α-galactose-N-acetyl galactosamine, α-mannose, α-(1-3)mannose, α-fucose, sialyl residues, and possibly α-glucose by 200 to 692% (n = 6, p < 0.05) and similar reactivity for β-galactose and β-galactose-N-acetyl galactosamine in secretions; in the glycocalyx, there was greater reactivity for β-galactose, β-galactose-N-acetyl galactosamine, α-(1-3)mannose, and sialyl by 209 to 700% (p < 0.05), but there were only minimal differences in the other glycoconjugates. Atropine prevented all effects of pilocarpine. These observations suggest that the secretions and the epithelial glycocalyx in sheep trachea have different glycoconjugate profiles. Muscarinic stimulation leads to profound but different alterations in both glycoconjugate profiles, which could influence the competing binding of the secretions and epithelium to bacteria colonizing the airway.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine