Search

Changes in calcium levels in organelles of the plasmodium of the myxomycete Physarum polycephalum were analyzed using the fluorescent calcium indicator chlortetracycline (CTC). Both the Ca2+-ATPase inhibitor 2,5;-di(tert-butyl)-1,4-benzohydroquinone (BHQ) (100 microM) and the calcium ionophore ionomycin (1 microM) induce a significant decrease in fluorescence level (by 30%) in CTC-stained microplasmodia; this is caused by release of calcium from intracellular storage compartments. An activator of ryanodine receptors, caffeine (10-50 mM), is less effective on Ca2+ release than BHQ or ionomycin, and their inhibitor, ryanodine (100 microM), almost completely blocks the response to caffeine, but only slightly decreases the effects of BHQ or ionomycin. Procaine, another inhibitor of ryanodine receptors, at 10 mM concentration completely abolishes both the BHQ and the ionomycin responses, but 50 mM is necessary to block the effect of 25 mM caffeine. These results suggest that both the BHQ- and the ionomycin-dependent Ca2+ releases occur through the ryanodine receptor and are to be considered as calcium-induced Ca2+ release (CICR). Both the ionomycin and the BHQ responses persist in the presence of Cd2+, which blocks Ca2+ channels of the plasmalemma. In most cases, Cd2+ itself induces release of Ca2+ from the CTC-stained calcium pool; the more effective Cd2+ is, the less the following ionomycin or BHQ responses occur. This indicates that Ca2+ entry through plasmalemma plays no significant role in the ionomycin- or BHQ-evoked initiation of CICR, and that the Cd2+- and BHQ/ionomycin-depleted Ca2+ stores overlap.

Molecular mechanisms of action of the total fraction of saponins from Red Korean Ginseng on the elements of the intracellular signalling system of the cells of ascitic Ehrlich carcinoma (AEC) were studied. The action of the total fraction of the saponins on the AEC cells was compared with that of the classic activator of such cells i.e. ATP. It was shown that the action of the total fraction of the saponins was similar to that of ATP. In concentrations of 10(-6) to 10(-3) per cent saponin induced an increase of [Ca2+]j mobilizing Ca2+ from the endoplasmic reticulum (ER) and activating the Ca2+ inlet to the cells. The same as in case with the use of ATP the Ca2+ mobilization from ER was reversible. In comparison to ATP saponin induced higher activation of the Ca2+ inlet to ER and the cells. The same as ATP saponin activated the Na+/H+ exchange and the Ca2+ - dependent K+-channels. Out of all the mention-ed parameters only the activation of the Ca2+ inlet to the cells was probably the direct result of the saponin action. The changes in the other parameters were mediated by nonspecific activation of the purine receptor. The analysis of the kinetic data demonstrated that unlike the ATP-dependent activation of the purine receptor the saponins first of all activated the inlet of Ca2+ to the cells and only after that the mobilization of the latter from ER.

During the experiment "Spore-ring Forming Fungi Biorhythm" of the Apollo-Soyuz test project the Rhythm-1 apparatus contained a dried film culture of bacteriophage T4Br+, growing cultures of Actinomyces and plastic nuclear particle detectors. The following were studied: the frequency of induction of r mutations in the bacteriophage film per 2 X 10(4) surviving particles, the spectrum of mutant types obtained (rI, rII, rIII), and the possible molecular mechanisms for the occurrence of rII mutants with due regard to the registered tracks of heavy nuclear particles. The studies showed that the local radiation due to heavy nuclear particle tracks plays a major role in space radiation damage.

A dried film culture of bacteriophage T4Br + was kept in a lead bioblock for 366 days under Alpine conditions at an altitude of 6100 m above sea level to study the genetic effect of space hadrons. In the gelatin-like film under study we discovered some film plots with markedly reduced bacteriophage survival. In such plots, the mutation frequency exceeded the spontaneous background mutation rate 60-100 times. The spectrum of r mutations as classified into standard groups rI, rII and rIII differed from that found for other model radiation systems such as gamma-ray radiation in buffer or nutrient broth, and hadron and HZE particle radiation under space flight conditions. Reversion analysis of 159 rII mutants showed that 54.4% had small and elongated deletions, 23.16% had point mutations, and 22.5% of all the mutants had both small deletion and point mutations.

A study was made of the effect of secondary radiation of 70 GeV protons on DNA of Chinese hamster cells. With a reference to fibroblast DNA, lymphoid cell DNA, and the lethal effect of radiation on the survival of Chinese hamster cells the RBE was 1.6-7.6, 1.1-3.8 and 1.14-1.7, respectively. DNA breaks were repaired to an equal level after exposure to secondary radiation from the accelerator and gamma-radiation from 60Co in equally effective doses.

It is shown that the RBE of the 70 GeV proton secondary radiation for the induction of single-strand break is 1.6-7.6 in Chinese hamster fibroblasts and 1.04-3.8 in limphoid cells and for the lethality of Chinese hamster cells 1.14-1.7. The RBE value increases with decreasing dose of the secondary radiation. On post-irradiation incubation of mammalian cells at 37 degrees C, single-strand breaks induced by the secondary radiation are repaired with the sane time course as those induced by gamma-rays. In our earlier works we have made an attempt to estimate the biological efficiency of radiation generated by the 70 GeV protons on bacteria, phage T4 and Vicia faba beans. The obtained values of the relative biological efficiency (RBE) of this radiation varied between 1.4 and 5.5, depending on the object, criterion of estimation, times of registration and other experimental conditions. The aim of the present work is to estimate the biological efficiency of synchrotron radiation by its effect on mammalian cells.

The effect of high energy (HZE) particles and high energy hadrons on T4Br+ bacteriophage was analyzed. The experiments were done in orbital flight, on high mountains, on an accelerator, and with an alpha particle source. We studied the survival rate of the bacteriophage, the mutation frequency, the mutation spectrum and the revertability under the action of chemical mutagens with a known mechanism of action on DNA. It was found that the biological efficiency of HZE particles and high energy hadrons is greater than that of gamma radiation. The spectra of mutations produced by these mutations and the mechanisms of their action are also different. These effects were local, because of the mode of interaction of the radiant energy with biological objects, and depended on the linear energy transfer (LET). The modes have now been experimentally defined.

Exponential survival curves were obtained for a dry film culture of bacteriophage T4 Br+ after exposure to both alpha-particles and gamma-quanta. Relative biological effectiveness of alpha-particles was 4.68 with respect to survival. The mutation spectrum after alpha-irradiation slightly differed from that produced by gamma-radiation.

It is generally accepted that heavy charged particles play an important part in generating the secondary flux of nuclear particles formed by the interaction of space hadrons with nuclei. It is assumed that these particles are responsible for the high biological efficiency of space hadrons in causing cellular damage by their strong interactions. To examine this assumption we investigated the effects of 5.3 MeV alpha particles on bacteriophage T4. This energy provides a LET value of 88.6 KeV/micrometer lying in the range of the highest biological efficiency.