Additivity in the sensitizing effects of nitrous oxide and oxygen

In earlier work, we proposed that nitrous oxide (N2O) and low concentrations of oxygen (10(-6) less than [O2] less than 10(-4) mol dm-3) share a common sensitizing mechanism. We also proposed that the basis for sensitization by N2O is different from that by high concentrations of oxygen ([O2] greater than 10(-4) mol dm-3). We have now tested these proposals with several Escherichia coli strains using mixtures of O2 and N2O. In the strains that are sensitized by N2O, we found that damage from low concentrations of O2 does not add to that from N2O. In contrast, we did find additivity in the sensitizing effects of N2O and high concentrations of O2. In those E. coli strains that are not sensitized by N2O, the effects of any concentration of O2 are the same in either N2 or N2O. These results are qualitatively the same as those from our previous study with E. coli B/r, and they support our proposals concerning similarities and differences in sensitizing mechanisms of N2O and O2.