Lung lamellar body amphiphilic topography: a morphological evaluation using the continuum theory of liquid crystals: I. Closed surfaces: closed spheres, concentric tori, and Dupin cyclides.

Abstract

The structure and symmetry of the bilayers of in vivo phospholipid lung lamellar bodies is shown to be analogous to thermotropic smectic-A liquid crystals and in vitro lyotropic multilamellar liquid crystalline liposomes. This structural similarity has led us to extend biophysical and geometrical principles that have long been used to predict the layer conformation in these in vitro systems to in vivo lung lamellar bodies. These configurations were demonstrated by electron micrographs of thin sections of rodent, monkey, and human lung lamellar bodies prepared by lipid-retaining embedment procedures. The bilayer configurations in all species were consistent with the two geometries predicted by minimal energy solutions of a continuum theory of liquid crystals subject to the boundary conditions imposed by the amphiphilic nature of lung surfactant lipid: concentric (either closed or partially closed) spheres and Dupin cyclides. These bilayer arrangements in lung lamellar bodies were virtually identical to the bilayer configuration of in vitro multilamellar liposomes. The agreement between the two predicted configurations and our observations shows that multilamellar liquid crystalline bilayer aggregate organization is universal in any aqueous environment.