Radioprotection of euoxic bacteria by phenothiazine drugs.

Survival studies on irradiated euoxic E. coli B/r cells in presence of various concentrations of four radioprotecting phenothiazine drugs have been carried out. Maximum radioprotection was obtained at a optimal concentration for each drug and it decreased on either side of it. The DNA strand break studies at the maximum protective and non-protective concentrations of chlorpromazine and promethazine revealed that the number of ssbs in DNA were less at the protective concentration which were efficiently repaired by the type-III repair process. On the other hand, at the non-protective concentrations, inhibition of DNA repair was noticed and a higher number of DNA ssbs were detected. We suggest that the membrane is fluidized to a greater extent at the protective concentrations allowing the chemical restitution of damaged sites by NPSH compounds. At the non-protective high concentrations of the drugs, the membrane may be too grossly disorganised to allow any repair and at the same time high concentrations of the drugs or their radicals may also react with radioprotective intracellular sulphhydryls.