The organism tolerance to extreme factors: physiological basis, regulation, prediction

The modern ideas about organism reactivity and tolerance, approaches to their estimation and prediction were observed in the paper. The ionizing radiation used as the basic factor, because this factor is the most convenient for the experimental investigation and experimental modeling of the different factors. The individual radiotolerance were observed as the reflection and the component of the organism general nonspecific tolerance. The enough voluminous of different physical factors combined influences were investigated, their reciprocally modified influences to the organism tolerance were estimated. The investigation of mammalian organism tolerance types and tactics of adaptation to the repeated influence of the stress-factors opens the new way to their estimation and prediction. The enough simple and reliable method of the individual tolerance (in particular, with used of the hormonal regulation system indices) were devised. This method is more effective than methods devised earlier.     

Content and structure of crew’s communicative behavior and gonadal hormone excretion during long-term chamber isolation of all-male international crew

The characteristics of psychophysiological adaptation to the simulation of the extended autonomous manned mission to Mars with limited resources and external communication were studied. The behavioral (communication with the external world) and physiological correlates of 105-day life and work in a pressurized compartment of the crew of six male subjects representing Russian and European space agencies under the conditions of sensory deprivation, confinement, monotony, and high autonomy were studied. Psychological, physiological, and biochemical (urinary cortisol and gonadal hormones) testing together with content analysis of the crew??s communication with the external world were made in parallel. The results confirmed, to a considerable extent, the preliminary hypothesis about the serious impact of stressful factors, including conflict, the significant decrease of the variety and scope of communication with the outer world, and social pressure on the verbal behavior and hormone levels in the future Martian crew. The correlation between the metabolism of the gonadal hormones and the volume, content, and creativity of the verbal human behavior during various stages of adaptation to the extended isolation in pressurized compartments has been discovered.     

Dynamics of the current front in a current-carrying plasma bridge

At the RRC Kurchatov Institute, high-impedance plasma opening switches have recently been developed that enable efficient pulse sharpening and are capable of operating in a repetitive mode. This paper presents the results of studying the conduction phase preceding the current break. In this stage, the magnetic-field and current waves propagate in the plasma from the switch to the load. The magnetic-field and current detectors placed along the plasma axis are used to measure the velocity and acceleration of the current front near the cathode and anode. At the end of the conduction phase, the characteristic velocities near the cathode and anode attain 100 and 50 cm/μs, respectively. During the current front propagation, the width of the front nearly triples. The acceleration and widening of the front are reasonably explained within electron magnetohy-drodynamics. It is shown that the voltage during the current break depends on the length of the coaxial cathode of the switch. When the cathode length is shorter than the distance covered by the current front, the generated voltage decreases substantially. __________ Translated from Fizika Plazmy, Vol. 27, No. 1, 2001, pp. 64–70. Original Russian Text Copyright ? 2001 by Dolgachev, Kingsep, Ushakov.     

Does Interaction between the Motor and Regulatory Domains of the Myosin Head Occur during ATPase Cycle? Evidence from Thermal Unfolding Studies on Myosin Subfragment 1

Myosin head (myosin subfragment 1, S1) consists of two major structural domains, the motor (or catalytic) domain and the regulatory domain. Functioning of the myosin head as a molecular motor is believed to involve a rotation of the regulatory domain (lever arm) relative to the motor domain during the ATPase cycle. According to predictions, this rotation can be accompanied by an interaction between the motor domain and the C-terminus of the essential light chain (ELC) associated with the regulatory domain. To check this assumption, we applied differential scanning calorimetry (DSC) combined with temperature dependences of fluorescence to study changes in thermal unfolding and the domain structure of S1, which occur upon formation of the ternary complexes S1-ADP-AlF₄ ^- and S1-ADP-BeF_x that mimic S1 ATPase intermediate states S1**-ADP-P_i and S1*-ATP, respectively. To identify the thermal transitions on the DSC profiles (i.e. to assign them to the structural domains of S1), we compared the DSC data with temperature-induced changes in fluorescence of either tryptophan residues, located only in the motor domain, or recombinant ELC mutants (light chain 1 isoform), which were first fluorescently labeled at different positions in their C-terminal half and then introduced into the S1 regulatory domain. We show that formation of the ternary complexes S1-ADP-AlF₄ ^- and S1-ADP-BeF_x significantly stabilizes not only the motor domain, but also the regulatory domain of the S1 molecule implying interdomain interaction via ELC. This is consistent with the previously proposed concepts and also adds some new interesting details to the molecular mechanism of the myosin ATPase cycle.     

Phase changes in the permeability of the mouse blood-brain barrier after uneven gamma-irradiation

Two phases of changes in blood-brain-barrier permeability for sour fuchsin have been observed in the early period after head or body irradiation at 2.58 C/kg: an increase (up to 2 h) and a decrease (from 2 to 6 h). The correlation between the decrease in BBB permeability and the frequency of clinical manifestations of radiation disease has been established. BBB permeability progressively increased later after head irradiation (24-120 h) which was indicative of its absolute dysfunction. The changes observed may reflect redistribution of fluid and electrolytes in the vascular bed and tissues leading to the onset of brain tissue edema.     

Study of response of Swiss Webster mice to light subunit of mushroom tyrosinase

The light subunit of mushroom, Agaricus bisporus, tyrosinase (LSMT), has been identified as an extrinsic component of the enzyme. Its function is unknown, but it can cross an epithelial cell layer, which suggests that it can be absorbed by the intestine. A similar capability has been demonstrated for the HA-33 component of the progenitor toxin from Clostridium botulinum, which is the closest structural homolog of LSMT. Unlike HA-33, LSMT appears to be non-immunogenic as shown by preliminary tests in Swiss Webster mice. We investigated the immunogenicity and histopathology of LSMT in mice to determine its safety in vivo. LSMT did not evoke generation of antibodies after prolonged periods of intraperitoneal administration. Histopathological observations confirmed the absence of responses in organs after twelve weekly administrations of LSMT. We found that LSMT is not toxic and is less immunogenic than the C. botulinum HA-33 protein, which supports further research and development for pharmaceutical application.