Fast response methods in the radiation chemistry of lethal damage in intact cells

The radiation-induced lethal damage in bacteria and mammalian cells involves some important chemical processes which extend up to about 10-2s after the initiating energy deposition. The gas explosion technique, analogous to the use of flash photolysis in photochemistry and pulse radiolysis in radiation chemistry, was applied to examine the kinetics of some of the fast processes within intact cells. The time resolution of this technique is about 100 μs. Five nanosecond electron pulses and the rapid transition from virtually anoxic (<5 ppm O2) to well oxygenated (>105 ppm O2) conditions can be used as the fast probes to determine the time scale of the radiosensitization by oxygen. The apparent differences between the observed intracellular kinetics of the reactions of O2 and of TAN (triacetoneamine-N-oxyl) with target damage and the reactions of these agents with DNA radicals support the view that O2 is not sensitized by reacting directly with DNA damage. In general, the processes described in this review appear to conform to simple bimolecular reaction kinetics. The intracellular reaction rates of the various agents tested are all slower than those expected from the rates of their reactions with radicals in dilute aqueous solution probably due to the complex structure of the cells. (Yamashita, S.)