A FREEZE‐FRACTURE STUDY OF TUBULAR MYELIN IN FETAL RABBIT LUNG

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Abstract
A freeze-fracture replication study was undertaken to clarify the relationship between intracellular lamellar bodies of type II alveolar epithelial cells and intra-alveolar contents in late gestation rabbit fetuses. The interior of inclusion bodies was composed of multiple stacks and/or whorls of membranes devoid of membrane-associated particles, while the limiting membrane of intracellular lamellar inclusion bodies was studded with membrane-associated particles of 150 .ANG. diameter. Intra-alveolar contents were comprised of 2 components; spherical bodies and tubular elements. Spherical bodies were identical to internal contents of lamellar bodies and were devoid of membrane-associated particles. Tubular elements mostly appeared rectangular on cross-fractured faces, but triangular and hexagonal forms were seen. These tubules rested on surfaces of spherical bodies and appeared to be formed of the outer lipid monolayer of spherical bodies. The tubular element of the alveolar contents apparently was formed through the interaction between the discharged lamellar body content and the alveolar fluid.