title: Rapid-mixing studies of radiosensitivity with thiol-depleted mammalian cells.
abstract: A moderate reduction in the non-protein thiol content of V79 379A Chinese hamster cells, obtained by pretreatment with buthionine sulphoximine (BSO), diethyl maleate (DEM) or N-ethyl maleimide (NEM), increase both the absolute radiosensitivity of the cells in hypoxia and the radiosensitizing effect of adding oxygen 7 ms after irradiation. Combined pretreatment of cells with BSO and NEM removes most of the non-protein thiol and some of the protein thiol; such treatment further increases the radiosensitivity of hypoxic cells but there is no further effect of adding oxygen 7 ms after irradiation. Addition of 2-mercaptoethanol to cells 7 ms after irradiation gives protection factors that increase with increasing severity of thiol depletion. Substantial radioprotection can still be observed when 2-mercaptoethanol is added 70 ms after irradiation of cells pretreated with BSO and NEM; there is no effect of adding 2-mercaptoethanol to such cells 50s after irradiation. These observations support the repair-fixation model of radiation damage and suggest that, in addition to the established role of non-protein thiol in chemical repair of radiation damage, other endogenous reducing agents such as protein thiol may be important in determining cellular radiosensitivity. A relatively long-lived thiol-modifiable component of radiation damage has been observed within hypoxic thiol-depleted cells.
mesh_terms: D000818:Animals; D019328:Buthionine Sulfoximine; D002460:Cell Line; D006224:Cricetinae; D005033:Ethylmaleimide / Q000494:pharmacology; D008298:Maleates / Q000494:pharmacology; D008623:Mercaptoethanol / Q000494:pharmacology; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives / Q000494:pharmacology; D010100:Oxygen; D011836:Radiation Tolerance; D011837:Radiation-Protective Agents / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000502:physiology*
chemical_list: D008298:Maleates; D011837:Radiation-Protective Agents; D013438:Sulfhydryl Compounds; D008717:Methionine Sulfoximine; D019328:Buthionine Sulfoximine; D008623:Mercaptoethanol; C014476:diethyl maleate; D005033:Ethylmaleimide; D010100:Oxygen