RADIATION. THE CELLULAR APPROACH
Expeniments were conducted on Escherichia coli to investigate the process of filament formation (elongation without cell division) which is known to occur following x irradiation. A study was made of the effects of x radiation admmistered at various dose rates for varying total dosages, as well as the effect of temperature on this process. Following x irradiation, bacterial cells showed a cessation of cell division without complete inhibition of growth. At the highest dose rates used (3080 rad/min), for a total dose of 30 krad, there was less growth while at lower dose rates (290 rad/min for a dose of 30 krad) the inhibition of cell division lasted longer. Filament formation was also evidenced when nonirradiated cells were incubated at 15 deg C. DNA synthesis was inhibited by x irradiation and was resumed sooner when higher dose rates were used. This was of particular interest in the light of previous evidence that cells receiving the higher dose rate of irradiation resumed cell division sooner. It is postulated that following x irradiation, cell membrane permeability was altered resulting in a change in the internal ionic milieu. Within certain limits of dose, sodium increased in the cell to a point where although growth still continued, synthesis of DNA was inhibited and cell division ceased. Chromatographic analysis of the media upon which x-irradiated cells of the protozoan Tetrahymena pyriformis were growing, indicated that transamination involving the production of alanine and aspartic acid was impaired. Thus an investigation of the effects of x rays administered at varying total dosages and varying dose rates on transamination was undertaken. Following x irradiation the cellular transaminase activity decreased. For doses in the mid-lethal range, maximum enzyme inhibition was observed at intermediate dose rates (1400 and 1800 rad/min) and minimal loss of activity at the highest and lowest dose rates (3000 and 600 rad/min). Complete recovery was not observed by the seventh transfer, with 15 deg and 25 deg postirradiation treatment. At 35 deg , however, there was a recovery to values equal to, or occasionally exceeding the control. These investigations indicated that dose, dose rate, and postirradiation incubation temperatures were important factors in modifying the response of cells to radiation as manifested by filament formation and changes in transaminase activity. (H.H.D.)
- Research Organization:
- Univ. of Toronto
- NSA Number:
- NSA-17-027136
- OSTI ID:
- 4697762
- Journal Information:
- Laval Medical (Canada), Vol. Vol: 34; Other Information: From Symposium on Radiosensitivity, Laval Univ., Quebec, Sept. 1962. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
Similar Records
Hydroxyl radical modify amino acids and prevent E. coli growth
Comparison of single-strand breaks in the DNA of rat thymocytes induced by irradiated histidine and. gamma. rays