Effects of Acid Aerosol Exposure on the Surface Properties of Airway Mucus

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Abstract
It was hypothesized that the mucous layer lining the tracheas of rats and guinea pigs contains surfactant material capable of lowering the air/mucus surface tension, γ, and that exposure to an irritant aerosol would raise the γ. The γ of the surface film was measured directly by a spreading droplet technique and indirectly by displacement of polymethyl methacrylate particles into the aqueous layer. The morphology of the mucous film was examined by electron microscopy after nonaqueous fixation. γ was 33.3 ± 0.70 (SE) mN/m and 32.3 ± 0.68 (SE) mN/m for the normal rat and guinea pig trachea, respectively. Exposure for 4 h to aerosols of sulfuric acid (94.1 ± 18.68 (SD) and 43.3 ± 4.57 (SD) mg/m3) caused a severalfold increase in thickness of the mucous layer with exudation of protein-like material. The osmiophilic surfactant film at the air/mucus interface became irregularly thickened and multilayered. Despite these morphological changes y remained low, 33.2 ± 0.43 (SE) mN/m and 32.6 ± 0.60 (SE) mN/m for rats and guinea pigs, respectively, and displacement of particles into the subphase was not compromised. The results indicate that rodent tracheas are able to maintain a low surface tension in the presence of injury.