Lung lamellar body amphiphilic topography: a morphological evaluation using the continuum theory of liquid crystals: II. Disclinations, edge dislocations, and irregular defects.

The bilayers in normal mammalian and human lung multilamellar bodies (LMB) are parallel, equally spaced, and continuous--a configuration that minimizes the large elastic strain energy associated with changing the equilibrium bilayer separation and the hydrophobic-hydrophilic repulsion energy between the hydrocarbon tails of phospholipid and the aqueous phase. This ideal behavior is disrupted at a limited population of large Burgers vector edge dislocations dissociated into +/- 1/2 disclination pairs. The configuration and interaction of the defects are explained by the continuum theory of liquid crystals and are shown to be identical to defects observed in in vitro surfactant liposomes and bilayers. We report the first observations with molecular resolution of the core structure of a liquid crystal dislocation. Defect cores are shown to be located between both headgroups and tailgroups in human LMB, suggesting that both types of core are similar in energy. This may be the result of partitioning of proteins or other nonlipid impurities in the LMB to the defect cores, which might also change the stability of the dislocations to favor their preservation. The edge dislocation defects interact in ways that minimize their overall strain energy. A population of edge dislocations may play an important role in the transport or localization of certain molecules through the lamellar body. Certain defects were observed in lung multilamellar bodies that have not been observed in in vitro systems; these are probably due to the complex, multicomponent nature of the LMB surfactant and the dynamic, in vivo environment of the LMB.