Viscoelastic properties of human tracheobronchial mucin in aqueous solution

Abstract

in Aqueous SolutionHuman tracheobronchial mucin isolatedfrom cysticjibrosis patients (CF HTBM) was purijied using a combination of geljiltration and density gradient centrifugation. The resulting mucin was fractionated to reduce polydispersity and to facilitate studies of the molecular weight dependence of mucin viscoelasticity in concentrated solution. The viscoelastic properties of CF HTBM were examined in distilled water, O.1M salt solutions and chaotropic solvents. In controlled strain experiments (strain 2 5%) with increasing mucin concentration, a crossover from sol to gel behavior is observed. The gel strength, as measured by the magnitude of the storage modulus at comparable mucin concentrations, is greatest for distilled water, intermediate for O.IM NaCl, and lowest for 6M GdnHCl. In distilled water, high molecular weight mucin undergoes a sol-gel transition at -12 mg/mL, and shows evidence of a plateau modulus at higher concentrations. The storage and loss moduli of concentrated high molecular weight fractions in 6M GdnHCl exhibit a power law dependence on frequency typical of weak gels near the sol-gel transition at 20 mg/mL. Similar rheology is observed in O.IM NaCl and 0.091M NaC1/3 mM CaCl,, but with evidence for additional weak associations at low frequency. The power law exponent in these systems is 0.70 k 0.02, in good agreement with prediction for networks formed by a percolation mechanism. Low molecular weight fractions in these solvents exhibit a fluidlike viscoelastic response. However, low molecular weight mucin in distilled water shows a strain-dependent increase in elasticity at low frequency indicative of weak intermolecular associations. Comparison of the rheological behavior of CF HTBM with our earlier studies of ovine submaxillary mucin lends support to the idea that carbohydrate side-chain interactions are important in the gelation mechanism of mucins. 0 1995 John Wiley & Sons, Inc.

The buffer capacity of airway epithelial secretions

“…Porcine gastric mucins did not buffer significantly at concentrations up to 1 mg/ml (Figure 7A), therefore mucins apparently contribute little to the buffer capacity of Calu-3 secretions. However in vivo the airway mucus is typically 2–3% solids (20–30 mg/ml), and dissolved mucins may reach ~12 mg/ml in the periciliary liquid, the concentration at which they undergo a sol-gel transition (McCullagh et al, 1995). When similar high concentrations of pig gastric mucins (e.g., 10 mg/ml) were titrated we obtained a β of ~5 mM/pH.…”

Calcium-dependent Protein Interactions in MUC5B Provide Reversible Cross-links in Salivary Mucus

“…These effects on tracer diffusion showed that native saliva contained a macromolecular organization that was sensitive to free calcium concentrations. This was supported by a major increase in the weight average molecular weight of the high molecular weight mucin fraction in saliva (10 -62 ؋ 10 6 ) and an increase in intrinsic viscosity of saliva (733 to 1203 ml/g) both caused by calcium. Analysis of the change in tracer diffusion in saliva showed a 20-fold increase in the apparent pore size (from 130 nm in 10 mM CaCl 2 to 2600 nm in 10 mM EGTA at physiological concentration).…”

Anionic poly(amino acid)s dissolve F-actin and DNA bundles, enhance DNase activity, and reduce the viscosity of cystic fibrosis sputum

“…These polyelectrolyte filaments contribute to the viscoelastic properties of CF sputum by affecting both viscosity and elasticity, as quantified by parameters such as the dynamic storage and loss shear moduli (GЈ and GЉ, respectively). The viscoelastic moduli of CF sputum can be significantly lowered by application of agents such as DNase I, which degrades DNA (19); gelsolin, which fragments actin filaments (26); or thiolreducing agents and NaCl that act directly on mucin (6,9,16).…”