Varied cytochrome oxidase activities of the alveolar type I, type II and type III cells in rat lungs: quantitative cytochemistry.

Cytochemically demonstrated cytochrome oxidase activities in mitochondria of rat pulmonary alveolar epithelial cells were quantitatively compared. As the standardized procedures, lungs were fixed for 10 min at 4 degrees C with 2% pure glutaraldehyde, and incubated for different times at 37 degrees C in a medium containing 1.0 mg/ml 3,3'-diaminobenzidine-4HCl, 1 mg/ml cytochrome c, 0.1 mg/ml catalase, 7% sucrose, and 0.1 M phosphate buffer, pH 7.4. Electron micrographs were then obtained, and the densities of the reaction deposits in the mitochondrial intermembrane-intracristal space were measured in an image analyzer, and were plotted in terms of time in minutes. The initial velocity (maximal rate) of the activity expressed as deposit accumulation rate (% area/60 min) filling the mitochondrial intermembrane-intracristal space of Type I, Type II and Type III cells was 40, 130 and 9.3, respectively. These results indicated that mitochondria are varied in the intensity of cytochrome oxidase activity among 3 types of pulmonary alveolar epithelial cells, and that the image-analyzing measurement of the accumulation rate of reaction product may be useful for quantitative analysis of enzyme activity, in particular, in the cells which are difficult to isolate from complex tissues.