NO2 interfacial transfer is reduced by phospholipid monolayers

Nitrogen dioxide (NO2) is a ubiquitous, pollutant gas that produces a broad range of pathological and physiological effects on the lung. Absorption of inhaled NO2 is coupled to near-interfacial reactions between the solute ga s and constituents of the airway and alveolar epithelial lining fluid. Alth ough alveolar surfactant imparts limited resistance to respiratory gas exch ange compared with that contributed by either the pulmonary membrane or upt ake in red blood cells, resistance to NO2 flux could have a significant eff ect on NO2 absorption kinetics. To investigate the effect of interfacial su rfactant on NO2 absorption, we designed an apparatus permitting exposure of variably compressed monolayers. Our results suggest that compressed monola yers enriched in 1,2-dipalmitoyl-sn-3-glycerophosphocholine present signifi cant resistance to NO2 absorption even at surface tensions greater than tho se achieved in vivo. However, monolayers composed of pure unsaturated phosp holipids failed to alter NO2 absorption significantly when compressed, in s pite of similar reductions in surface tension. The results demonstrate that phospholipid monolayers appreciably limit NO2 absorption and further that monolayer-induced resistance to NO2 flux is related to physicochemical prop erties of the film itself rather than alterations within the aqueous and ga s phases. On the basis of these findings, we propose that pulmonary surfact ant may influence the intrapulmonary gas phase distribution of inhaled NO2.