Quantitative three-dimensional reconstruction and carbohydrate cytochemistry of rat nonciliated bronchiolar (Clara) cells.

We have employed three-dimensional reconstructions and cytochemistry to analyze nonciliated bronchiolar epithelial (Clara) cells from rat lungs. We identified a previously unreported ovoid granule type, which was characterized by its relative electron-lucency and eccentric electron-dense core. These electron-lucent granules were less common than electron-dense granules and were polarized toward the Golgi. They occupied 0.51% of the cell volume. Quantitative analysis of cell volume fractions showed the more numerous electron-dense granules to be polarized toward the air border; they occupied 2.5% of the cell volume. Periodic acid-thiocarbohydrazide-silver protein staining for hexose sugars indicated no differences between the granule types with regard to their carbohydrate content. Multivesicular bodies occupied 0.42% of total cell volume and were distinctly polarized toward the surface of the Golgi. Rod-shaped granules were present in 4 of the 6 reconstructed cells, ranging in number from 0 to 9 per cell. Nine apparent secretory events were seen in 6 cells and all appeared as exocytosis. We conclude that rat Clara cells contain at least 3 morphologically distinct granule types located in different volumes of the cell, and that exocytosis is the mode of secretion. The functional relationship between the ovoid granule types could include precursor-product lineage or different secretory products. We suggest that multivesicular bodies and light granules are stages in dark granule genesis.

Duke Scholars

Author Stephen Lowe Young Medicine, Pulmonary, Allergy, and Critical Care Medicine