FINE STRUCTURAL IDENTIFICATION OF PEROXISOMES IN MOUSE AND RAT BRONCHIOLAR AND ALVEOLAR EPITHELIUM

Following incubation in Novikoff and Goldfischer's alkaline modification of Graham and Karnovsky's diaminobenzidine (DAB) medium, densely stained bodies were identified in the bronchiolar nonciliated cells (Clara cells) and in type II alveolar cells (great alveolar cells, granular pneumonocytes) in mouse and rat lung. In Clara cells, the electron-dense reaction product was distributed in spherical, single membrane-bound bodies having an average diameter of 0.3-0.4 µ but varying from 0.15-0.65 µ. Neither nucleoids nor crystalline cores were seen inside these structures. These bodies were seen to be often closely associated with rough endoplasmic reticulum cisternae. The electron-lucent vesicles, some of them with a dense core, previously reported as secretion granules, never stained with DAB. The DAB-stained bodies present in type II alveolar cells had a somewhat different morphology. They were often elongated, with an average size of 0.2-0.3 x 0.1 µ but varying between 0.6 and 0.08 µ. The electron density of their staining was the same as in the DAB-positive bodies of Clara cells. Both cell types were studied for acid phosphatase activity; the distribution pattern of the reaction was entirely different from the one reported above. Considering the specificity of this modified reaction and the effect of inhibitors, it is assumed that the DAB-stained bodies present in both Clara and type II alveolar cells—in spite of a slightly atypical aspect in the latter—are peroxisomes.