The periodicity and architecture of lipid retained and extracted lung surfactant and its origin from multilamellar bodies

Abstract

Lipid and carbohydrate retaining procedures were utilized to retain these components of surfactant in thin section. The origin of tubular myelin surfactant from multilamellar bodies was postulated on morphological evidence to be : an expansion of lamellae in pairs caused by the absorption of a homogeneous, probably carbohydratebased, material of undetermined origin; immediately after the pairs expanded to 438 Å, the lamella (lipid bilayer) that was most peripheral in the multilamellar body underwent a molecular rearrangement to form the two cross lipid bilayers; the four lipid bilayers formed a square tubule 413 Å of side and 0.16–1.8 μ long. The homogeneous material included within each tubule (the surfactant matrix) did not completely fill the intratubular space, but a centrally located, spherical, 57 Å diameter, electron transparent, area was observed. The 413 Å square tubules were separated on all sides by a 25 Å fatty acid tail area. The phospholipid head areas were 46 Å and the surfactant matrix was 132 Å between the electron transparent, center area and the phospholipid heads layer. Extraction with several organic solvents was also studied: slight ethanol extraction—alteration of surfactant matrix and loss of transparent, central area. Moderate ethanol extraction—alteration of surfactant matrix to form artifactual tubules and filaments, disruption of lipid bilayers. Severe extraction—ethanol produced loss of integrity of both matrix and lipid bilayers; vinylcyclohexane dioxide or methacrylate produced complete loss of all lipid bilayers, but surfactant matrix retained tubular configuration ; DMP-30 produced complete loss of lipid bilayers, and although most of the matrix material was retained, all areas appeared fractured and randomly oriented.