Effects of an alkane on the adsorption and collapse by the lipids of pulmonary surfactant.

Pulmonary surfactant adsorbs rapidly to the surface of the liquid layer that lines the alveolar air sacs of the lungs. When compressed by the decreasing alveolar surface area during exhalation, the adsorbed films avoid collapse from the air/liquid interface and reduce surface tension to exceptionally low levels. Results with factors that induce surfactant lipids to increase intrinsic curvature suggest that adsorption proceeds via a curved rate-limiting structure. Samples with negative intrinsic curvature, defined by a concave hydrophilic surface, adsorb rapidly, but they also desorb quickly. Prior reports show that by optimizing chain packing, n-tetradecane (td) can promote conversion of planar bilayers to the negatively curved cylindrical monolayers of the inverse hexagonal phase without changing intrinsic curvature. The studies here show that td increases the rate of adsorption by the complete set of surfactant lipids without affecting intrinsic curvature and without promoting desorption of the adsorbed film during compression.