“Anoxic” radiation response in cultured mammalian cells

There have been recent expressions of caution concerning the adequacy of methods of oxygen removal from biological systems under test for anoxic radiation response. Baker and Town (1966) and Michael, Scott and Révész (1966) have reported that the time for liquid-gas equilibration requires hours. These communications did not contain information on cell survival to radiation during the time-course of gassing. The purpose of this letter is to present results of experiments with cultured Chinese hamster cells (V79–103A) which bear on some of the questions raised by these authors. A known number of single cells were plated on to 9 cm glass Petri dishes and allowed to grow overnight to an average colony multiplicity (N) of approximately 1·7. At the time of irradiation, medium was removed from the dish and the latter, without its cover, was placed in a holder similar to that reported by Elkind and Sutton (1960). The amount of residual medium was less than 0·5 ml. The holder allowed for temperature control below and gas control above the dish.