ABSTRACT
Nitrous oxide reacts during irradiation to increase the yield of .OH, a radical many believe to be a major cause of lethality. Logically, one would expect N2O to be a radiation sensitizer. In some instances it is, while in others it is not. In some cases we can explain why N2O fails to sensitize; factors such as dose rate, cell concentration, buffer composition and ionic strength all influence when N2O will sensitize and, if it sensitizes, by what magnitude. Based on the results presented here with multiple strains of procaryotic and eucaryotic cells, we believe the anoxic sensitivity is another critical factor that governs whether N2O will sensitize. Our data, with data from the literature, show a relationship between the anoxic sensitivity and the N2O enhancement ratio. N2O does not sensitize in vitro unless the anoxic sensitivity (inactivation constant, k) is less than approximately 0.2 daGy-1.
Subject(s)
Nitrous Oxide/pharmacology , Oxygen/physiology , Radiation Tolerance/physiology , Radiation-Sensitizing Agents/pharmacology , Animals , Cell Line , Cell Survival/drug effects , Cell Survival/radiation effects , Dose-Response Relationship, Radiation , Escherichia coli/drug effects , Escherichia coli/radiation effectsABSTRACT
Although nitrous oxide (N2O) is often a radiation sensitizer in procaryotic cells, it fails to sensitize some strains of bacteria, some yeast strains, and most eucaryotic cell lines. At present this inconsistency cannot be satisfactorily explained. The experiments here use eight strains of E. coli, some of which are not sensitized by N2O, to test the hypothesis that N2O's failure to sensitize might be based on high thiol content or on low peroxidase activity. Our data contradict those hypotheses. In addition, further data show that the strains not sensitized by N2O contain no unique cellular component or compound which blocks damage from N2O.
