SURFACE-PROPERTIES, MORPHOLOGY AND PROTEIN-COMPOSITION OF PULMONARY SURFACTANT SUBTYPES

Separation of surfactant subtypes is now commonly used as a parameter in assessing the amount of active compared with inactive material in v arious models of lung injury. The protein content, morphology and surf ace activity were determined of the heavy and light subtype isolated b y differential centrifugation. Here we report the presence of surfacta nt proteins B and C in the heavy subtype but not in the light subtype. Adsorption studies revealed that separation of fast adsorbing broncho alveolar lavage resulted in slowly adsorbing heavy and light subtypes. Surfactant, reconstituted from heavy and light fractions, did not sho w a high adsorption rate. It is concluded that the isolation procedure s might result in a loss of fast adsorbing surfactant structures. Surf ace area cycling was used as a model in vitro for the extracellular su rfactant metabolism The heavy subtype is converted into the light subt ype during conversion. Conversion performed with resuspended heavy sub type revealed the generation of a disparate subtype. Furthermore it wa s found that the conversion was dependent on preparation and handling of the samples before cycling. Finally, adsorption studies at low surf actant concentrations revealed a delayed adsorption of lipid-extracted surfactants compared with natural surfactants. These observations emp hasize the importance of the (surfactant-associated protein A-dependen t) structural organization of surfactant lipids in the adsorption proc ess.