Abstract
Cell killing of X-rays is caused by direct action and indirect action. Two thirds of the effects are caused by indirect action under oxic condition. However, there are few reports on the effects under anoxic condition.
We examined here contribution of indirect action under anoxic condition for cell killing. CHO cells were irradiated by X-rays (200kVp, 20mA) under oxic and anoxic conditions. Protective effect of DMSO that specifically caught OH radicals was estimated from the cell survival. Fractions of indirect action through OH radicals were calculated the contribution of the action using a method by Shinohara et al. (Acta Oncol., 35, 869-75. 1996).
The portion in contributions of indirect action under oxic and condition was approximately 70%. However, it decreased to be 60% when cells were irradiated under hypoxic condition. G(OH) value is independent with oxygen concentration (C. V. Sonntag, The Chemical Basis of Radiation Biology, 33. 1987). The difference of contribution of the action between oxic and anoxic conditions may be explained that oxygen participates in reaction with OH radicals and DNA.
