Electron Microscope Study of the Alveolar

Alveolar brush cell (Type III alveolar cell) was found in the alveolar lining epithelium of the adult rat.1'1 ' Meyrick and Reid first de-scribed its morphological characteristics using a transmission electron microscope (TEM).1 '" In our previous study using a scanning electron microscope (SEM) as well as transmission electron microscope (TEM), surface structure of the alveolar brush cell was shortly demon-strated.J) Ultrastructural features of the al-veolar brush cell are: (1) the cell having only a narrow free surface exposed to the alveolar lumen, and most of its surface is covered with thin sheet-like cytoplasmic processes of Type I epithelial cell, (2) small free area showing many regular straight microvilli, 0.9-1.2 /xm in length and a diameter of about 0.2 fitn, which protrude into the alveolar lumen, and (3) widely distrib-uted fine filaments, many vacuoles 50-100 nm in diameter and aggregated granules of glyco-gen in the cytoplasm.1'1 ' These morphologi-cal characteristics of the alveolar brush cells suggest that these cells seem to be responsible for some chemoreceptive function in the al-veolar duct.1'4"0 ' The increase in population of the alveolar brush cell was also observed after the injection of Bleomycin sulphate known to induce epithelial metaplasia as well as lung fibrosis.T'8) In this study, further investigation on the relationship between alveolar brush cell and Type I and II alveolar cells was carried out using SEM. Materials and methods. Five male rats of the Wistar strain weighing 150 g, or 4-week-old ones were injected intraperitoneally with Fig. 1. Proliferation of the alveolar brush cell is observed within a vascular ring (arrow) in a rat 24 hr after the treatment. Several Type II cells and an alveolar brush cell are also observed beside a vascular ring. These cells are completely distinguished from respiratory bronchioles. x 1,20