Secretion of Lamellar Bodies in Type II Pneumocytes in Organoid Culture: Effects of Colchicine and Cytochalasin B

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Abstract
Lamellar bodies are the morphological correlate to the alveolar surface-active agent. Diminished synthesis of this surfactant in newborns results in the respiratory distress syndrome. Secretion of lamellar bodies and its dependence on the cytoskeleton are not yet well understood and are still controversially discussed in the literature. We therefore used an organoid culture system of fetal mouse lung cells to investigate electron microscopically secretion of lamellar bodies and influence of both colchicine and cytochalasin B on the secretion process. Secretion of lamellar bodies is to be considered as an eccrine secretion, because no other cytoplasmic components were extruded. It includes a very fast component in opening of the secretory vacuole. Synthesis, but not secretion, was inhibited by colchicine; secretion, but not synthesis, was inhibited by cytochalasin B. Furthermore, formation of the histotypic structures in vitro and deposition of the basal lamina were disturbed by cytochalasin B, but not altered by colchicine. After short-term treatment, these effects turned out to be reversible. The results indicate that synthesis of lamellar bodies depends on an intact microtubular system, whereas secretion requires actin filaments in a functional state.