A new type of cell in the pulmonary epithelium of the newt Triturus alpestris Laur. A scanning and transmission electron microscopic study.

Single cells of a new type appear scattered among pneumocytes in the pulmonary epithelium. The surfaces of these cells communicate with the air space and display numerous finger-like microvilli. In comparison to pneumocytes, these cells have a more lucid cytoplasm and their apical parts contain large amounts of electron-lucent vesicles and electron-dense granules, which are probably released into the lumen of the lung. These secretory cells exhibit a yellow formaldehyde-induced fluorescence, which suggests that they belong to the class of APUD cells.