IN-VITRO STUDY OF CILIARY BEAT FREQUENCY AFTER SHORT-TERM EXPOSURE OF SO2 AND NO2

Mucociliary transport is an important defense mechanism of the respiratory tract. The aim of this study was to investigate the effect of SO2 and NO2 at different concentrations on ciliary beat frequency (ZSF). Single ciliated cells were obtained from 25 volunteers by nose brush. ZSF was quantified using video-interference-microscopy. The cells were placed on a polycarbonate membrane, which was in contact with the surface of a reservoir filled with RPMI medium (bicarbonate buffered) or electrolyte solution (Ringer), allowing the cells to be supplied by capillarity. In an exposure chamber the cells were exposed for 30 to 120 min to SO2 2.5 to 15.0 ppm at 37-degrees-C. SO2 induced a dose dependent decrease in ZSF of the cells, supported by Ringer solution. 2.5 ppm SO2 caused a 42.8%, 12.5 ppm a nearly 100% decrease (8.10 +/- 0.24 vs. 0.28 +/- 0.20 Hz). ZSF of cells cultured in RPMI medium was reduced moderately after 12.5 PPM SO2 exposure (7.90 +/- 0.26 vs. 6.66 +/- 0.31 Hz). In Ringer solution we observed a decrease of pH after 30 min SO2 exposure with 12.5 ppm to a minimum value of 3.6. hi marked contrast, the pH of RPMI medium remained constant at 7.5 under identical conditions. After adding RPMI medium to Ringer solution, ZSF increased in parallel to the pH (5.0 ppm: 2.77 +/- 0.37 to 7.97 +/- 0.49 Hz). After an initial increase in ZSF, 120 min NO2 exposure to 15.0 ppm yielded a decrease in ZSF of 23.3% under conditions of constant pH. These data suggest that the highly water soluble SO2 abolishes ZSF by decreasing the pH of the tissue culture medium. One possibility for the NO2 induced reduction in ZSF is oxidative damage of cell surface structures mediated by this reactive gas.