The alveolar lining layer is thought to consist of a continuous duplex layer, i.e., an aqueous hypophase covered by a thin surfactant film which is a monolayer with dipalmitoyl-phosphatidylcholine (DPPC) as its most important component. Findings obtained by electron microscopy and results from in vitro experiments suggest, however, that the structure and hence the structure-function relations of surfactant films are more complex. In order to better define their structures films of surfactants were studied by scanning force microscopy.Four different surfactants were spread on a Langmuir-Wilhelmy balance, and then transferred onto a solid mica plate by the Langmuir-Blodgett technique, under various states of film compression. Imaging of the films by scanning force microscopy was performed in the contact (repulsive) mode in air.The scanning force micrographs revealed that surfactant films are not homogeneous, but rather undergo phase transitions depending on the surface pressures. Even at comparable surface pressures different surfactants show quite different surface patterns. Differences in surface structure can even be observed in films containing surfactant proteins (SP)-B and SP-C.These observations give further evidence that the widely accepted hypothesis of a regular monolayer of phospholipids governing the surface tension probably does not hold true, but that the structure-function relationship of surface active surfactant films is even more complex than hitherto thought. Eur Respir J 1999; 14: 1290±1296. According to a widely accepted hypothesis the alveolar lining layer has the following structural properties: it is a continuous duplex layer consisting of an aqueous hypophase covered by a thin surfactant film, and the surfactant film is a monolayer with dipalmitoyl-phosphatidylcholine (DPPC) as its most important component [1±4].There are numerous studies of the structure of the lining layer, all of which are fragmentary. Indeed, the sample preparation and preservation of this delicate structure for microscopy is extremely difficult; there is no standard to distinguish between facts and artefacts [5], and it is not easy to conceive of how monolayers of saturated phospholipids can be preserved and visualized by the usual fixatives [6]. As to the first condition, i.e., the existence and continuity of a duplex layer, GIL and WEIBEL [7] were the first to convincingly demonstrate a two-phase lining layer by transmission electron microscopy. However, the film was often fragmented and disposed in patches, and could not be detected on flat parts of the alveolar walls. Although studies of freeze-fractured preparations suggested its continuity [8], the exact structure of the lining layer has remained a matter of debate. More recently, BAS-TACKY et al. [9] have clearly demonstrated the continuity of the lining layer by low-temperature electron microscopy, and improved tissue preparations have also resulted in a better visualization of the film such that all of the evidence now available suggests a continuum...
Aim-To investigate the influence of bilirubin on the surface tension activity of a porcine derived (Curosurf) and synthetic (Exosurf) surfactant.Methods-The captive bubble surfactometer at phospholipid doses of 0.5 mg/ml (low dose) and 1 mg/ml (high dose) in solutions of increasing bilirubin concentrations (0.25, 0.5, and 1.0 mg/ml) was used.Results-Curosurf (without bilirubin) showed a higher surface tension activity than Exosurf, as shown by area compression of 30 (SD 0.6)% compared with 76(1.4)% at low surfactant dose and 25 (0.9)% compared with 85 (0.5)% at high dose (P<0.01). Bilirubin showed negligible surface activity at the concentrations studied. At low phospholipid dose (0.5 mglml Curosurf), bilirubin increased film area compression of lipid extract surfactant from 30 (0.6)% to 55 (1.6)%, 59 (0.1)%, and 68 (0.5)% at the three studied bilirubin concentrations, respectively (P<0.01). At high phospholipid dose (1 mg/ml Curosurf), bilirubin had the same adverse, although less pronounced, effect on film area compression of porcine lipid extract surfactant (25 (0.9)% vs 26 (0.9)%, 39 (1.3)%, and 44 (1.1)%, respectively) (P<0.01). Using synthetic surfactant (Exosurf), with a much lower original surface activity, bilirubin did not further inhibit its surface tension properties at any of the phospholipid doses studied. Conclusion-These results indicate that in vitro bilirubin impairs the surface tension activity ofporcine lipid extract surfactant, but does not affect synthetic surfactant activity. (Arch Dis Child 1996;75:F191-F196)
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