RESUMEN
In experiments with wild-type diploid yeast cells of Saccharomyces cerevisiae, the synergistic interaction of ultraviolet (UV) light (wavelength, 254 nm) and heat (45--60 degrees C) was studied both for mutagenic and inactivation effects. Simultaneous hyperthermia and UV light treatments increase the frequency of UV-induced mitotic intergenic recombination (crossing-over) and cell inactivation. The enhancing effect was a function of UV light fluence rate. It is concluded that the effect of hyperthermia on low fluence UV or high fluence UV irradiation results in comparable effects on survival and mitotic recombination suggesting similar modulation by hyperthermia of the effects induced by UV at different fluence rates. The interpretation of the data obtained was carried out within the widely accepted point of view considering the synergistic effects as a result of repair ability damage.
Asunto(s)
Mitosis/genética , Recombinación Genética , Saccharomyces cerevisiae/genética , Muerte Celular/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Calor , Saccharomyces cerevisiae/efectos de la radiación , Factores de Tiempo , Rayos UltravioletaRESUMEN
A new mathematical model for the synergistic interaction of lesions produced by ultraviolet (UV) light and high temperature has been proposed. The model suggests that synergism is expected from the additional lethal lesions arising from the interaction of sublesions induced by both agents. These sublesions are considered noneffective after each agent is taken alone. The model predicts the dependence of the synergistic interaction on the ratio of lethal lesions produced by each agent applied, the greatest value of the synergistic effect as well as the conditions under which it can be achieved, and the dependence of synergistic effect on UV light fluence rate. These predictions of the model have been tested for the simultaneous combined action of UV light (wavelength 254 nm) and heat (45-57.5 degrees C) on two strains of wild-type diploid yeast cells of Saccharomyces cerevisiae. The theory appears to be appropriate and the conclusions valid.
Asunto(s)
Calor , Saccharomyces cerevisiae/efectos de la radiación , Rayos Ultravioleta , Relación Dosis-Respuesta en la Radiación , Modelos Teóricos , Saccharomyces cerevisiae/citología , TemperaturaRESUMEN
Synergistic effects of simultaneous application of ultraviolet (UV) light and hyperthermia on survival and recombination of diploid yeast cells were studied. For both test-systems the dependence of the synergistic interaction on UV light fluence rate and exposure temperature was revealed: the temperature range synergistically increasing the action of UV light is shifted towards low temperature values with decreasing of UV light fluence rate. For cell survival, the dependence of the synergistic enhancement ratio on the exposure temperature passes through a maximum. A possible qualitative interpretation of these results is discussed.
Asunto(s)
Recombinación Genética/fisiología , Recombinación Genética/efectos de la radiación , Saccharomyces cerevisiae/fisiología , Saccharomyces cerevisiae/efectos de la radiación , Relación Dosis-Respuesta en la Radiación , Temperatura , Rayos UltravioletaRESUMEN
Methodology approach demonstrating a principle importance of mutual increase of damaging action of physical and chemical environmental factors at low doses and intensities was described. A generalize conceptual basis of synergism was suggested which was appropriate both for combined action of ionizing radiation with other agents and for combined action of any other harmful environmental factors. The main idea of the concept described here is in the formation of additional effective damages under combined action due to interaction of sublesions induced by every agent and which are not effective under separate action of each agent employed. Mathematical presentation of this concept allowed to make some new non-trivial conclusions. It was shown theoretically the existence of optimal ratio of damages induced by acting agents under which the highest synergism must be obtained. The effect of synergistic interaction has to be dependent on intensities of agents: the less intensity of one agent used, the small intensity of another factor must be applied for the greatest synergistic effect expression. The test of these consequences was performed for a number of experiments described in this paper. The results presented here have of principle importance for interpretation of the higher effectiveness of low dose and dose rate of ionizing radiation observed in some cases.