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[en] The objective of this research was to investigate the dose-response relationship with regard to the lethal and mutagenic effects of exposure of cells to radon and its decay products. Dose-rate dependence was studied, as well as the nature of the DNA lesions. The effect of DNA repair on the lethal and mutagenic effects of exposure and on the character of the DNA lesions was investigated by comparing the response of L5178Y strains that differ in their ability to rejoin X radiation-induced DNA double strand breaks. The nature of radon/radon daughter-induced mutational lesions in human lymphoblasts was also investigated

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[en] The experiment performed in vitro intended to examine whether an adaptive response could be elicited on lymphocytes by low-level contamination of whole blood with tritiated water and if the modification of the dose rate has any influence on it. Lymphocytes pre-exposed to ³HOH (0.2 - 6.6 MBq/ml) and subsequently irradiated with I Gy γ-rays showed micronuclei frequency significantly lower (40% - 45%) than the expected member (sum of the yields induced by ³HOH and γ-rays separately). The degree of the radioresistance induced by HTO pre-treatments became higher with decreasing dose-rate for a rather similar total adapting dose. In vivo, the aim of the study was to investigate if different dose rates are inducing modulation of the lipid peroxidation level and of the thymidine uptake in different tissues of animals contaminated by HTO ingestion. The total doses varied between 5 and 20 cGy and were delivered as chronic (100 days) or acute contamination (5 days). It was observed that only doses about 20 cGy caused a dose-rate dependent increase of the lipid peroxidation level in the tissues of small intestine, kidney and spleen. Both chronic and acute contamination did produce reduced incorporation of thymidine in the cells of bone marrow. The most effective decrease of thymidine uptake was induced by the acute contamination in the lower dose domain (approx. 5 cGy). Our hypothesis is that in this dose domain the modification of thymidine uptake could be due to changes at the level of membrane transport. (author)

[en] At the tandem accelerator laboratories in Munich and Erlangen vertical beamlines were installed last year. The advantage of a vertical beamline is that cells can be irradiated in a medium at 37 C and with simultaneous gassing, therefore also in physiological conditions. First experiments were carried out at the accelerator in Munich with a proton energy of 25 MeV. Chinese Hamster cells B14 were irradiated in Petri dishes where the base was of 1 mm polystyrol or 2 μm hostaphan foils. The cell survival was measured by the cell survival assay and the repopulation of the colonies by the total colony volume. A solution of DNA with protein was irradiated to study DNA double strand breaks by constant field gel electrophoresis and DNA protein crosslinks by the nitrocellulose filter assay. For cell survival, total colony volume and DNA double-strand breaks X-rays and protons gave corresponding results, while with protons, higher yields of DNA-protein crosslinks were observed than with X-rays. (orig.)

[en] We have investigated the effectiveness of heavy ions in the induction of chromosomal aberrations in mammalian cells by the recent technique of fluorescence in situ hybridization (FISH) with whole-chromosome probes. FISH-painting was used both in metaphase and interphase (prematurely condensed) chromosomes. The purpose of our experiments was to address the following problems: (a) the ratio of different types of aberrations as a function of radiation quality (search for biomarkers); (b) the ratio between aberrations scored in interphase and metaphase as a function of radiation quality (role of apoptosis); (c) differences between cytogenetic effects produced by different ions at the same LET (role of track structure). (orig./MG)

[en] From several studies of hyperthermia there have been reports that hypoxic cells are more sensitive to heat than their oxic counterparts. Experimental techniques in this investigation eliminated the effect of pH, trypsinization and cell attachment, when assaying the effect of hyperthermia on cells. Under hypoxic conditions, HeLa S₃ and Chinese hamster cell-lines did not have an increased sensitivity to heat compared with oxic cells. HeLa S₃ cells were protected against heat by hypoxia. Light-microscopy indicated the rupture of the plasma membrane, occasional nuclear budding, membrane vesicles and granulation of cell contents after heating at 43⁰C for 3 hours. Scanning electron micrographs showed that cells were more rounded after heat treatment and that there was an accompanying decrease in the number of microvilli, suggesting that the mechanism of cell attachment was affected. Heated cells should be delicately handled and subjected to the minimal trauma so that an accurate comparison of survival can be made. (author)