[en] Nuclear dimensions in mammalian cells appear as a determining factor of chromatin organization and cellular radiosensitivity. Most radioresistant interphase cells have a nuclear volume (Vsub(n)) of 75 to 2700 μm³, that could allow both the topological organization of chromatin as loops attached to the inner surface of the nuclear envelope and the unfolding of condensed molecules. In contrast, the radiosensitive small lymphocytes, with Vsub(n) values of 20 to 65μm³, seem to comprise significant amounts of highly condensed chromatin and dispose of an uncompleted topological organization of DNA, which may cause their incapacity to perform replication and transcription of DNA as well as the repair of radiation damage at a cell level. The indications are that radiosensitivity (1/D₃₇) of animal cells, containing a similar quantity of DNA, should be directly proportional to 1/nuclear volume (1/Vsub (n)). However, DNA is unevenly distributed within the nuclear space, according to a partial ordering of interphase chromosomes; and it appears that radiosensitivity increases in zones of high DNA or chromatin density. (author)

[en] Letter to the editor

[en] A simple mathematical model of DSB distributions in DNA from irradiated interphase eukaryotic cells is considered and an approximate description of resulting DNA sedimentation profiles is derived. The model takes into account the differences found between the radiosensitivities of heterochromatin and euchromatin and is based, contrary to the usual approach, on a non-homogeneous distribution of DSB in eukaryotic DNA. Comparison with some experimental DNA sedimentation profiles prefers the proposed model to the common one. At the same time a greater radiosensitivity difference (at least in yeast cells for the present) has been established in anoxic conditions compared to aerobic ones. (author)

[en] Ionizing radiation is a special group of toxic agents whose general interaction can be calculated. This was demonstrated using a radiation interaction model previously published. In this paper, this model is refined and mathematically reformulated using a unified set of assumptions. It postulates the existence of a common intermediate lesion and the relative action of lesions before, at and after this common stage. General quantitative dose-effect of relationships of mixed radiations can be derived from the dose-effect relationships of the components in the mixture. (author)

[en] Studies of transport across the plasma membrane in intact cells frequently involve measuring the incorporation of a labelled extracellular species into the cells. Unfortunately, if the labelled species is metabolized in the cell, the kinetics of labelling are made more complicated. Using the example of the incorporation of ³²P-labelled orthophosphate into cells, we describe a mathematical model which allows for this complication, and show how this may alter the interpretation of experiments. The anlysis is widely applicable to cellular labelling studies with any species that undergoes chemical exchange with a large cellular pool. (author)