Ultrastructure of the nonciliated bronchiolar epithelial (Clara) cell of mammalian lung: II. A comparison of horse, steer, sheep, dog, and cat.

The researchers compared certain features in the lung cells of five different mammals: horses, steers, sheep, dogs, and cats. They found common structures in the horse and sheep, while the steer, dog, and cat differed significantly.

Methodology

• The subject of the research were the nonciliated bronchiolar epithelial cells, specifically looking at the agranular endoplasmic reticulum (AER) – a cell component involved in protein synthesis and lipid metabolism – and membrane-bound avoid granules.
• The researchers selected five animals commonly used in pulmonary research – horse, steer, sheep, dog, and cat. They looked at the lungs of these animals and prepared them using standard fixation via airway infusion and selective embedding techniques for examination under electron microscopy.

Results

• The nonciliated bronchiolar epithelium of the horse and sheep had numerous avoid granules (averaging more than 15 per cell) and abundant agranular endoplasmic reticulum (AER).
• In contrast, granules were scarce in steers and dogs (averaging less than 2 per cell) and entirely absent in cats. AER was much less abundant in these three species compared to horses and sheep.
• Another notable finding was that the main feature within the cytoplasm – a jelly-like substance that fills a cell – differed across species. Glycogen, a form of energy storage in animals, dominated the cytoplasm of the steer, dog, and cat cells. It was variable in sheep and rare in horses.
• Only cat cells exhibited large mitochondria – the “powerhouse” of a cell – with few cristae (internal compartments) and densely staining matrix, a substance within the mitochondria.

Conclusion

• The researchers concluded that the nonciliated bronchiolar cells of horses and sheep had similar structural features to the same cell types found in common laboratory mammals – abundant granules and AER.
• Meanwhile, in steers, dogs, and cats, these cells were structurally different, having far fewer granules and minimal AER. This could implicate differences in the lung cell function across species.

This study implies the careful selection and use of animal models in pulmonary research, as differences in the cellular structure may affect the applicability of findings across different species.