Modification of radiation effects in single-cell systems by membrane-binding agents.

Chlorpromazine sensitized E. COLI B/r, thymocytes and Yoshida ascites-tumour cells to 60Co gamma-rays, preferentially, under hypoxic conditions, Residual sensitization was observed in E. coli B/r. The radiosensitization by chlorpromazine was found to be due to the reaction of radiolytically-induced hydroxyl radicals with the sensitizer. When both procaine HCI and chlorpromazine were present during anoxic irradiation of E. coli B/r, there was no additive effect. But the addition of procaine HCL after irradiation to cell sensitized by chlorpromazine had an effect that was significantly greater than that produced even by oxygen. A similar effect was observed when lignocaine or tetracaine was used in place of procaine. The possible mechanisms involved in radiosensitization by chlorpromazine and in the post-irradiation effect of local anaesthetics in cells sensitized to 60Co gamma-rays by chlorpromazine are discussed.