Isolation and characterization of highly radioresistant malignant hamster fibroblasts that survive acute gamma irradiation with 20 Gy.

To study the acquired radioresistance of tumor cells, a model system of two cell lines, Djungarian hamster fibroblasts (DH-TK-) and their radioresistant progeny, was established. The progeny of irradiated cells were isolated by treating the parental cell monolayer with a single dose of 20 Gy (PIC-20). The genetic and morphological features, clonogenic ability, radiosensitivity, cell growth kinetics, ability to grow in methylcellulose, and tumorigenicity of these cell lines were compared.

Photobiological modulation of cell attachment via cytochrome c oxidase.

The number of cells attached to glass substrates increases if HeLa cell suspensions are irradiated with monochromatic visible-to-near infrared radiation (600-860 nm, 52 J m(-2)) prior to plating. The well-structured relationship between this biological response and the radiation wavelength (action spectrum with maxima at 620, 680, 760, and 820 nm) suggests the existence of a photoacceptor responsible for the enhancement of attachment (presumably cytochrome c oxidase, the terminal enzyme of the respiratory chain) and, secondly, the existence of signaling pathways between the mitochondria, the plasma membrane, and the nucleus of the cell. Treating the cell suspension with ouabain (a Na(+), K(+)-ATPase inhibitor), amiloride (an inhibitor of N(+)/H(+) exchangers), or sodium azide (a cytochrome c oxidase inhibitor) prior to irradiation significantly modifies the action spectrum of cell attachment enhancement.

[Retention of tumorigenicity in radioresistant progeny of cells surviving exposure to high doses of gamma irradiation].

The cell tumorigenic ability and the cell clonogenicity in semi-solid medium of highly radioresistant variant cell line, PIC-20 (the progeny of djungarian hamster fibroblast cell line DX-TK- surviving acute exposure to 20 Gy of gamma-irradiation), were examined. In the absence of additional radiation, no differences between tested features of non-irradiated PIC-20 cells and parental DX-TK- cells were observed. On the contrary, after gamma-irradiation with high doses the essential differences in the properties of the examined cell lines were revealed.

[Different levels of radiation protection in tumor cell population].

It is postulated the presence of various systems of protection in tumor cell population. This systems have different mechanisms and are induced by the level of damage. From the analysis of the literature and own experiments the author maintains that there are not less than three levels of tumor cell population protection.

Cell attachment to extracellular matrices is modulated by pulsed radiation at 820 nm and chemicals that modify the activity of enzymes in the plasma membrane.

Background And Objectives: Adhesive interactions between cells and extracellular matrices play a regulative role in wound repair processes. The objective of this investigation is to study action mechanisms of pulsed radiation at 820 nm on cellular adhesion in vitro. Light emitting diodes (LED) at 820 nm are widely used for treatment of wounds of various etiology.

[Small doses of ionizing radiation as radiation modifying factor].

To investigate the biological effects of small dose ionizing radiation has been acquiring greater importance. The awareness of how and in what direction it show its modifying effects in small doses is an essential scientific basis for developing standards, living conditions under specific environmental conditions. Cultured Hela cells and DEF 4/21 fibroblasts were used to evaluate the biological effects of small-dose ionizing radiation, by examining the conditions under which it showed its modifying effect in small doses (0.

Donors of NO and pulsed radiation at lambda = 820 nm exert effects on cell attachment to extracellular matrices.

The adhesion of HeLa cells to a glass matrix was evaluated after the irradiation of the cell suspension with a pulsed near-infrared light-emitting diode (lambda = 820 nm, frequency 10 Hz, dose 8-120 J/m(2)) and treatment with two donors of nitric oxide, sodium nitroprusside (SNP, 5 x 10(-4) M) and NaNO(2) (4 x 10(-4) M). It was found that in an irradiated cell suspension, the cell-glass adhesion increases in a dose-dependent manner (a bell-shaped curve with a maximum at 60 J/m(2)). The treatment of cells with SNP or NaNO(2) before the irradiation eliminates the radiation-induced attachment stimulation.

Cell attachment modulation by radiation from a pulsed light diode (lambda = 820 nm) and various chemicals.

Background And Objective: Adhesive interactions between cells and extracellular matrices play a regulative role in wound repair processes. The objective of this investigation is to study the mechanisms of light action on cellular adhesion in vitro. The adhesion of HeLa cells to a glass matrix is evaluated after irradiation with a pulsed near-infrared (IR) diode and treatment with various chemicals.

[Systemic radiation reaction of tumor cell populations to high dose irradiation].

The work presents the results of the experiments confirming supposition of existence of a protection mechanism opposing hard destruction effects and acting at cell population level. The experiments were carried out with cultures of tumour cells HeLa and DEF 4/21. By technique of hybrid selection in selective HAT medium it was found that radioinduced cell fusion led to formation of viable and clonogenic cell hybrids.

[The appearance of a fracture of radioresistant cells in a fibroblast population irradiated at high doses].

Two sublines of Djungarian DEF 4/21 hamster cells survived after gamma irradiation with the doses of 10 and 20 Gy were obtained. The survived cell posterity (SCP) of both cell lines are considerably more clonogenic. They show a higher proliferative activity and a shorter period of generation than the control cells.

[The effect of gamma irradiation under different regimens on isolated and contacting cells of a HeLa culture].

It was shown that isolated and united HeLa cells in culture responded to single irradiation and repeated low dose irradiation by different ways. The effect on radiosensitivity was revealed in united cells only.

Effects of monochromatic low-intensity light and laser irradiation on adhesion of HeLa cells in vitro.

Background And Objective: The adhesion of HeLa cells was evaluated after irradiation with monochromatic low-intensity light or laser irradiation. It is well known that the cell-cell and cell-matrix adhesion changes during wound repair. For better understanding of low-power laser light action on the wound healing process, it would be of interest to study the light action on cellular adhesion in vitro.

Irradiation with He-Ne laser increases ATP level in cells cultivated in vitro.

A monolayer of HeLa cells was irradiated with an He-Ne laser (632.8 nm, 100 J m-2, 10 s) and the amount of adenosine triphosphate (ATP) was measured by the luceferin-luciferase bioluminescent assay technique at different times (5-45 min) after irradiation. The amount of ATP in the log phase of cultured cells remained at the control level (0.

Irradiation with He--Ne laser can influence the cytotoxic response of HeLa cells to ionizing radiation.

A monolayer of HeLa cells in plateau-phase of growth was exposed to He--Ne laser radiation (632.8 nm, 100 J/m2) either 5, 60 or 180 min before gamma-irradiation (0.2-10 Gy, 6.

[The kinetics of polykaryon formation in a HeLa cell culture after irradiation at doses of 5 and 10 Gy].

Monolayer culture of HeLa tumor cells irradiated at 5 Gy and 10 Gy doses was followed up in kinetics for 14 days. It was shown that starting with day 3 the cell monolayer is modified in such a way that some cells occur in 2- to 8-cell accumulations. The rate of formation of such groups and the number of cells in them were dose-related.

[The effect of He-Ne laser radiation on the adhesive properties of the cell membrane].

Changes in the number of individual cells and cellular complexes after a standard dispergation procedure were used as a criterion for evaluating the strength of the cellular contacts at various time-points after the irradiation of HeLa monolayers with a He-Ne laser (100 J/m2, 10 W/m2, 10 s). The per cent of cellular complexes increased after the irradiation, being maximal (19.5 +/- 0.

[Changes in the amount of ATP in HeLa cells under the action of He-Ne laser radiation].

Amount of ATP in HeLa cells in various phases of growth was measured after He-Ne laser irradiation (100 J/m2, 10 W/m2, 10 s) by a bioluminescent luciferin-luciferase method. In cells of the exponential phase of growth, the amount of ATP (basal level 8 x 10(-16) mole/cell) starts to increase in 15 min after the irradiation with a maximum (170% above the basal level) at 20 min, and then decreases gradually to the basal level. The sensitivity of the cells to He-Ne laser radiation is lowest in lag-phase of growth, then increases to a plateau (approximately 185% above the control level) from 5th day of cultivation.

Evidence for formation of somatic cell hybrids in a population of irradiated cells.

Experiments using two genetically marked lines of Djungarian hamster cells (DM-15 HPRT- and DH-TK-) and the technique of hybrid selection in selective HAT medium revealed viable colonies in a mixed culture irradiated with a dose of 5 Gy. The sublines grown from these colonies were examined. Chromosome analysis showed that about 45% of those cells were hybrids inheriting chromosome markers of both parent strains.

[The formation and viability of hybrid cells in a population after irradiation at lethal doses].

With the use of two genetically labeled lines of Djungarian hamster cells and the method of hybrid selection on a HAT-selective medium it was found that in the irradiated mixed culture of the above cell lines, cells were formed that survived in the conditions of total destruction of irradiated parent cells. The chromosome analysis showed that about 45% of the survived cells were hybrids resulting from the radiation-induced fusion of two initial cell lines. These hybrid cells were capable of reproduction.