Inverse dose-rate effect of DNA breaks and inactivation of transforming activity induced by tritiated water and 60Co gamma-rays.
When an aqueous solution of plasmid DNA at a constant low concentration of 5 micrograms/cm3 was irradiated with 60Co gamma-rays, D37 dose of single-strand breaks was decreased from 18 Gy at a dose-rate of 6.77 Gy/h of acute irradiation to 2.3 Gy at a dose-rate of 0.00212 Gy/h. Or G value was increased from 0.0010 to 0.0081. Similar dose-rate dependency of D37 dose and G value were also found when the plasmid DNA solution was treated with various concentrations of tritiated water at various dose-rates, ranging from 5.13 Gy/h to 0.000118 Gy/h. RBE of tritium beta-rays for single-strand breaks was ranged from 0.3 to 0.5 in a wide range of dose-rates. When the DNA solution was saturated with argon to remove oxygen, the dose-rate dependency of gamma-rays was abolished and that of tritium beta-rays was significantly suppressed. When the DNA solution in air was kept at 4 degrees C for 50 h or 25 days after acute irradiation, the G value of DNA breaks was the same as that kept at -20 degrees C for the same period, but much lower than that of the solution irradiated for the same period at a lower dose-rate to give the same total doses. This shows that the inverse dose-rate effect could not be induced from the different exposure periods but from continuous irradiation of different dose-rates. The inverse dose-rate effect for inactivation of transforming activity of DNA irradiated with tritiated water was also observed in the range from 0.0588 Gy/h to 0.00118 Gy/h.
Takakura
K
K
Department of Physics, College of Liberal Arts, International Christian University, Tokyo, Japan.
Ishikawa
M
M
Minegishi
A
A
Sakai
K
K
Okada
S
S
D003037:Cobalt Radioisotopes; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D006878:Hydroxides; D017665:Hydroxyl Radical; D014169:Transformation, Bacterial / Q000528:radiation effects*; D014316:Tritium / Q000494:pharmacology*; D014867:Water / Q000494:pharmacology*
D003037:Cobalt Radioisotopes; D004277:DNA, Single-Stranded; D006878:Hydroxides; D014867:Water; D014316:Tritium; C033961:tritium oxide; D017665:Hydroxyl Radical