Ion-dependent Inactivation of Barium Current through L-type Calcium Channels

It is widely believed that Ba²⁺ currents carried through L-type Ca²⁺ channels inactivate by a voltage- dependent mechanism similar to that described for other voltage-dependent channels. Studying ionic and gating currents of rabbit cardiac Ca²⁺ channels expressed in different subunit combinations in tsA201 cells, we found a phase of Ba²⁺ current decay with characteristics of ion-dependent inactivation. Upon a long duration (20 s) depolarizing pulse, I_Ba decayed as the sum of two exponentials. The slow phase (τ ≈ 6 s, 21°C) was parallel to a reduction of gating charge mobile at positive voltages, which was determined in the same cells. The fast phase of current decay (τ ≈ 600 ms), involving about 50% of total decay, was not accompanied by decrease of gating currents. Its amplitude depended on voltage with a characteristic U-shape, reflecting reduction of inactivation at positive voltages. When Na⁺ was used as the charge carrier, decay of ionic current followed a single exponential, of rate similar to that of the slow decay of Ba²⁺ current. The reduction of Ba²⁺ current during a depolarizing pulse was not due to changes in the concentration gradients driving ion movement, because Ba²⁺ entry during the pulse did not change the reversal potential for Ba²⁺. A simple model of Ca²⁺-dependent inactivation (Shirokov, R., R. Levis, N. Shirokova, and E. Ríos. 1993. J. Gen. Physiol. 102:1005–1030) robustly accounts for fast Ba²⁺ current decay assuming the affinity of the inactivation site on the α₁ subunit to be 100 times lower for Ba²⁺ than Ca²⁺.     

Individual optimization: Mechanisms shaping the optimal reaction norm

In general, optimal reaction norms in heterogeneous populations can be obtained only by iterative numerical procedures (McNamara, 1991; Kawecki and Stearns, 1993). We consider two particular, but biologically plausible and analytically tractable cases of individual optimization to gain insight into the mechanisms which shape the optimal reaction norm of fecundity in relation to an environmental variable or an individual trait. In the first case, we assume that the quality of the environment (e.g. food abundance) or the quality of the individual (e.g. body size) is fixed during its entire life; it may also be a heritable individual trait. In the second case, individual quality is assumed to change randomly such that the probability distribution of quality in the next year is the same for the parent and for her offspring. For these two cases, we obtain analytical expressions for the shape of the optimal reaction norm, which are heuristically interpretable in terms of underlying selective mechanisms. It is shown that better quality may reduce the optimal fecundity. This outcome is particularly likely if better quality increases a fecundity-independent factor of parental survival in a long-lived species with fixed quality. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological Adaptations in Juvenile Dolly Varden <Emphasis Type="Italic">Salvelinus malma</Emphasis> (Salmonidae) Dwelling in Polluted Rivers of Kamchatkan Volcanic Territories

Biochemical status of riverine juvenile Dolly Varden was defined under the dissolved toxicants and mineral suspension excess concentration impact. The processes of toxicants bioaccumulation, metabolism activation, dynamics of oxidative stress and detoxification were examined in a wide range of natural chronic pollution intensity. Background conditions variability and critical toxicants levels in the polluted habitats were determined. Physiological response specificity was found for juveniles of anadromous and landlocked Dolly Varden.     

Wheat root colonization by Azospirillum brasilense strains with different motility

Migration of associative bacteria Azospirillum brasilense in semisolid media is performed mainly by swarming (Swa⁺ phenotype), which depends on the flagellar functioning and intercellular contacts. Non-swarming mutants of A. brasilense Sp245 lacking a polar flagellum migrate in semisolid media with microcolony formation using a unrevealed mechanism (Gri⁺ phenotype). The study of wheat root colonization dynamics demonstrated that A. brasilense Sp245 Gri⁺ mutants exhibited lower capacity for wheat root adsorption. However, after “anchoring” has occurred, both A. brasilense Sp245 and its Swa-Gri⁺ mutants colonized the growing roots with virtually the same efficiency. All strains under study formed microcolonies on the surface of roots, stimulated root branching, and exhibited changes in the composition of protein antigens exposed on the bacterial cell surface. Indirect evidence was obtained for enhanced production of genus-specific protein antigens in the process of A. brasilense Sp245 adaptation to growth on plant roots.     

Toroidal Alfvén eigenmodes in a tokamak with a population of high-energy large-orbit ions

The effect of the density gradient of high-energy ions moving in large magnetic drift orbits is studied analytically in the context of the problem of toroidal Alfvén eigenmodes (TAEs) in a tokamak. It is found that, when the population of such ions is not too small, this effect can substantially modify standard TAEs and give rise to new types of TAEs, which are called TAEs-H, TAEs-H⁺s, and TAEs-H^?s. The continual dissipation of TAEs is investigated with allowance for the effect in question. It is shown that the dissipation acts to dampen all the TAE types under consideration.     

Interaction of plasma clouds produced from two laser targets

Results are presented from studies of the interaction of two plasma clouds produced from two different-type laser targets in an ambient gas in the MKV-4 stand of the Iskra-5 facility. The experimental data are compared with the results of numerical simulations.     

Methodological approaches to the evaluation of physical efforts during work (a review of soviet literature)

Present-day methods of evaluation of physical loads, widely used in laboratory studies and in industry and implemented by direct assessment and indirect determination of the amount of efforts made by the hand, are reported. The analysis of literary data testifies to the advisability of wide use of the methodological approach to the evaluation of efforts proposed by the authors which permits recording the efforts of the hand in N and differentiating them according to their application immediately at the time of work independent of the character of the manual instrument used as well as without using any instrument. The measuring of efforts, their amount, and duration, with the aid of the proposed method together with the evaluation of the functional state of the groups of muscles engaged in work, offers the possibility of revealing the causes of industrial fatigue and overstrain leading to pathological changes in the neuromuscular apparatus of the hands, of prognosticating occupational diseases both under the conditions of the actually existing processing equipment and at the stage of planning new technology and developing pilot production.     

Development of hybrid human interferon alfa-2 strain-producers and the use of enteropeptidase for production of N-terminal methionine-free interferons

We developed a technique for production of human interferon-α2a (IFN-α2a) and IFN-α2b lacking the N-terminal methionine. First of all, we constructed plasmids containing genes of hybrid IFN-α2 controlled by different promoters; the proximal part of the genes incorporated various sequences encoding the enteropeptidase cleavage site. As a result, four strains of Escherichia coli producing hybrid IFN-α2 were obtained. The protocol for IFN-α2 renaturation, cleavege of its N-terminal part, and chromatographic purification of the N-terminal methionine-free IFN-α2 was developed.