Effects of exposure to NO2 on dome formation in alveolar epithelial cell monolayers

Primary cultured monolayers of rat Type II pneumocytes were used to investigate the effects of NO2 on alveolar epithelial barrier properties. Such monlayers form fluid-filled domes which are thought to result from active solute transport from medium to substratum, with water following passively. Using dome formation as a transport marker, 5-day-old cultures were directly exposed to 30 ppm NO2 in 5% CO2/air at 25 degrees C by cyclically tilting culture plates from side to side such that both halves of the monolayer were exposed during each cycle. Exposures consisted of 10 cycles of 4 min each (2 min per side), for a cell exposure time of 20 min. Control plates were simultaneously exposed to 5% CO2/air under identical conditions. Twenty-four hours after exposure, NO2-exposed monolayers exhibited significant decreases in dome density and individual dome volume as compared to controls. By 48 hr postexposure, differences between NO2-exposed and control values were less but remained significant. Control monolayers were essentially unaffected by exposure to 5% CO2/air. These results show that short-term sublethal exposures to NO2 produce a decrease in dome formation in Type II alveolar epithelial cell monolayers. This finding is most likely due to a decrease in the active transepithelial sodium transport rate and/or an increase in the permeability of cell membranes or tight junctions.