Ultrastructure of the Nonciliated Bronchiolar Epithelial (Clara) Cell of Mammalian Lung: I. A Comparison of Rabbit, Guinea Pig, Rat, Hamster, and Mouse

TLDR

The nonciliated bronchiolar epithelial (Clara) cell is defined by abundant agranular endoplasmic reticulum and numerous membrane‑bound ovoid granules. This study aimed to quantitatively and qualitatively assess the ultrastructural homogeneity of Clara cells across laboratory mammals. Tissue from adult male rabbits, guinea pigs, rats, hamsters, and mice was fixed by airway infusion at 30 cm H₂O, selectively embedded, and bronchioles were examined by electron microscopy. All five species displayed ovoid granules and abundant AER, but granule abundance was highest in rats, lowest in hamsters, with hamsters having the largest granules; granule density was uniform except in guinea pigs, AER was widespread in hamsters and apical in others, and mitochondrial morphology varied, indicating considerable interspecies variation.

Abstract

AbstractTwo morphologic characteristics have been used to define the nonciliated bronchiolar epithelial cell: (1) abundance of agranular endoplasmic reticulum (AER) and (2) numerous membrane-bound ovoid granules. To quantitatively and qualitatively assess the ultrastructural homogeneity of this lung cell type among laboratory mammals used in lung research, we examined tissue from adult male rabbits, guinea pigs, rats, hamsters and mice. Following fixation by airway infusion at constant pressure (30 cm H2O), lungs were processed by a selective embedding technique and bronchioles of known anatomic location were examined by electron microscopy. Nonciliated bronchiolar epithelium of all five species contained ovoid granules and abundant AER. Granules were most abundant in the rat (11.1 ± 8.8 per cell) and least in the hamster (4.4 ± 5.2 per cell). Granules were largest in hamster (0.72 ± 0.25 μm) versus 0.44 μm or less in the other species. Granules were of uniform electron density except in the guinea pig. AER was found throughout the cell in hamster and restricted to apical regions in others. Large spherical mitochondria with few cristae were present only in mice, rabbit, and guinea pig. We concluded that there was considerable interspecies variation in abundance, size, and morphology of the granules, in abundance and distribution of AER; and in mitochondrial morphology.