The effects of NO₂ on ionic surface charge on Type I pneumocytes of hamster lungs

Pinocytotic vesicles have been found to be common organelles throughout the cytoplasm of Type I pneumocytes. The number of uncoated vesicles were increased in response to acute exposure to NO₂. These uncoated vesicles endocytosed horseradish peroxidase. In this study, the aim was to determine plasma membrane surface properties which were induced by NO₂ exposure on the Type I pneumocytes of hamster lungs. Cationic ferritin and ruthenium red were used as ionic surface probes. Transmission electron microscopy was performed on thin sections of lung tissue fixed in vivo by vascular perfusion with glutaraldehyde after exposure to NO₂ and cationic ferritin. Tissues exposed and fixed were also treated with cationic ferritin or ruthenium red. Transmission electron microscopic examination of glutaraldehyde-fixed Type I pneumocytes demonstrated both coated and uncoated vesicles. Cationic ferritin, which normally binds sparingly to control Type I pneumocytes, had a high affinity for the plasma membranes of Type I pneumocytes after NO₂ exposure. Many of the binding sites were associated with vesicles on the basis of presence of bound cationic ferritin in developing and formed vesicles. Cationic ferritin was also observed in vesicles adjacent to and on the basal lamina in the lungs from hamsters incubated with ferritin for 30 minutes. This indicated that the ferritin is transported across the epithelium by the uncoated vesicles. Ruthenium red, another cationic molecule, was found in the same sites as the cationic ferritin. The data showed that NO₂ induced a change in the ionic surface charge, which may have contributed to the formation of uncoated pinocytotic vesicles.