Modification of radiation response of E. coli B/r cells by phenothiazines.

Promethazine and trimeprazine sensitized anoxic E. coli B/r cells to 60Co gamma-rays, but both drugs showed a radioprotective effect under euoxic conditions. Their radiosensitizing effect was found to be due to the reaction of radiolytically induced hydroxyl radicals with the sensitizers. The radioprotective effect of these drugs is attributed to changes in the membrane structure conducive with chemical repair of the damaged sites in the gel region of the cellular membrane by intracellular sulphydryl compounds. Pre-irradiation depletion of sulphydryls from E. coli B/r by treatment with N-ethyl maleimide abolished the radio-protective effect of these drugs under euoxic conditions.