Potentiation of radiation effects in hypoxic HeLa cells

HeLa cells were irradiated with two doses of gamma rays: the first dose was delivered under hypoxic conditions and the second dose was delivered under oxygenated conditions. Increased inactivation of cellular proliferative capacity as a function of intervening time was obtained when hypoxic conditions were maintained between doses. Hypoxic protection from ionizing irradiation can be counteracted by manipulating postirradiation conditions.