MOLECULAR MOBILITY IN THE MONOLAYERS OF FOAM FILMS STABILIZED BY PORCINE LUNG SURFACTANT

Certain physical properties of a range of foam film types that are bel ieved to exist in vivo in the lung have been investigated, The contrib ution of different lung surfactant components found in porcine lung su rfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and t hickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using th e fluorescence recovery after photobleaching technique. Fluorescent ph ospholipid probe molecules in foam films stabilized by porcine lung su rfactant samples or their hydrophobic extracts consisting of surfactan t lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhi bited more rapid diffusion than observed in films of its principal lip id component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effe ct appears to be due to contributions from minor lipid components pres ent in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfac tant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant prote ins in the sample reduced the diffusion coefficient (D) of the lipid a nalog in the adsorbed layer of the films, Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying abo ve the heating curve, However, in cases where some surface molecular a ggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobi lized. The thickness. size, capillary pressure, configuration, and com position of loam films of lung surfactant prepared in vitro support th eir investigation as realistic structural analogs of the surface films that exist in vivo in the lung. Compared to other models currently in use, foam films provide new opportunities for studying the properties and function of physiologically important alveolar surface films.