Том 61, № 5 (2016)

The Escherichia coli Dps protein belongs to a specific family of bacterial ferritins; it is a nanosized particle that contains an inorganic core (~5 nm in diameter) and a protein shell with a size of 8–9 nm. The protein shell consists of 12 identical subunits with the known crystal structure of a dodecamer. The composition and structure of the core have been less studied. The core formation is associated with the oxidation products of Fe2+ ions in the ferroxidase centers of the protein. Thus, Fe2O3 oxides are the main compounds of the core. However, the mineralization properties of Fe2+ ions under anaerobic conditions in vitro may indicate a more complicated composition of the core in the native Dps protein. This paper presents a technique for the preparation of purified Dps samples for ultrahigh vacuum synchrotron experiments by X-ray absorption near edge structure spectroscopy of the iron absorption edge in the soft X-ray region. The conducted synchrotron experiments have revealed the presence of both trivalent and divalent iron ions in the octahedral and tetrahedral environment of oxygen atoms in the prepared biological samples. This points to a complex ionic composition of the core even in the native Dps protein, which has been isolated from aerobically grown bacteria.

For many years, myoglobin was considered as an intracellular globin involved in oxygen transport and storage in cardiac and skeletal muscles. Following the discovery of its ability to convert nitrite into nitric oxide during hypoxia, myoglobin was shown to play a new role in the hypoxic signaling pathway that regulates mitochondrial functions of the electron-transport chain. This review presents experimental evidence that supports this concept and discusses the significance of this newly reported ability for cardiac and skeletal muscle functions.

The inotropic effect of Pr³⁺ and La³⁺ ions on the heart muscle of frog Rana ridibunda, as well as the influence of the ions on respiration, swelling, and the potential (ΔΨ_mito) on the inner membrane of Ca²⁺- loaded rat heart mitochondria, energized by glutamate and malate or succinate in the presence of rotenone were studied. It was found that 2 mM Pr³⁺ in Ringer’s solution reduces the force of spontaneous contractions and those induced by electrical stimulation in the heart; it had a negative chronotropic effect, decreasing the frequency of spontaneous contractions. Pr³⁺ and La³⁺ prevented a decrease in the 2,4-dinitrophenol (DNP)- uncoupled respiration of energized rat heart mitochondria, swelling of these organelles in salt media, and a reduction in ΔΨ_mito on the inner mitochondrial membrane that were induced by Ca²⁺ ions. Retardation by Pr³⁺ and La³⁺ ions of these calcium-induced effects may suggest that in the inner mitochondrial membrane these metals inhibit the opening of the mitochondrial permeability transition pore caused by Ca²⁺ overload of mitochondria. The data we obtained are important for a better understanding of the mechanisms of the damaging action of rare-earth elements on Ca²⁺-dependent processes in the vertebrate myocardium.

The aim of this work is to clarify the role of the electrical activity of the Physarum polycephalum plasmodium in the control of the contractile activity and self-organization of the directed locomotion. This single-celled organism with a non-excitable membrane is a classic object that is used in studies of amoeboid motility. Its patterns of motor behavior and signal systems are common for many tissue cells. The presence of 50 mM KCl in an agar substrate under half of a separate plasmodial strand strongly inhibits the formation of the frontal zone and leads to sharp morphological polarization of the strand, which suggests the involvement of electrical processes in the autowave self-organization of the plasmodial structure. The gigantic sizes of the plasmodium make it possible to record its electrical activity simultaneously at different parts of the cell. It has been established that potentials and currents at parts of the plasmodium that are distant from each other oscillate synchronously and differ only in the shape of the signals, probably due to differences in the phases or the number of excited harmonics. We recorded currents (~50 pA) of single ion channels of the plasmodial membrane using the classical local voltage-clamp method. It has been found that the oscillation spectrum of the current that is generated by the plasmodium has high-frequency fluctuations, which are probably connected with periodic detachments of the membrane from the cytoskeleton during the formation and growth of the pseudopodia. It has been also shown that neomycin, a substrate inhibitor of phospholipase C, prevents oscillations of both the mechanical and electrical activity of the plasmodium. This is consistent with its well-established ability to inhibit mechanosensitive Ca²⁺ channels, which are apparently present in the plasmodial membrane. These data indicate the presence of a general signal system that is linked with the dynamics of the membrane- cytoskeleton association, which could be involved in the galvano- and chemotaxis of amoeboid cells.

The functional properties of the spinal-cord structures of experimental rats under a 7-day gravitational unloading were assessed using the method of transcranial magnetic stimulation. Hypogravity was modeled by hanging the animals by their tails in an antiorthostatic position. The gastrocnemius muscle potentials evoked by magnetic stimulation of the efferent structures of the spinal cord were registered. We found that gravitational unloading causes significant changes in motor-potential parameters and the central motor transmission time. We propose that the cause of the revealed transformations is afferent inflow limitation, first of all the motor type, as well as adaptation of the central nervous system to new conditions of motor activity.

Mechano-calcium feedbacks that provide fine tuning of electrical and calcium activation of the heart muscle to mechanical conditions of contractions are an important element of electromechanical coupling as a key mechanism of the autoregulation of the contractile activity of the myocardium. A large quantity of experimental and theoretical evidence supports the cooperative dependence of the calcium-troponin complex kinetics on the cross-bridge concentration as a principal mechanism that underlies the mechano-calcium feedback in the intact myocardium. At the same time, experiments performed using skinned myocardial preparations have demonstrated that mechanical conditions significantly affected only the calcium sensitivity of the Ca²⁺–force relationship rather than its Hill coefficient of cooperativity. These data make some investigators doubt the contribution of cooperativity to the mechano-calcium feedbacks. To overcome these arising discrepancies, we propose an improved conception of cooperativity that reveals the extent of intensity differently in the steady state and in transitional processes. The proposed conception enables us to reproduce and explain both the mechanodependence of calcium activation in the intact myocardium and the results with skinned muscle within the framework of a mathematical model.

The aim of this study was to assess the response of key mTORC1 substrates to a bout of contractile stimuli under different times of functional unloading. Functional unloading of hind-limb muscles was carried out by the method of antiorthostatic suspension. Twenty-eight Wistar rats were divided into four groups: control, and hindlimb suspension for 1, 3, and 7 days. After hindlimb suspension, isolated soleus muscles of rats were subjected to a bout of ex vivo eccentric contractions. The contents of phosphorylated forms of p70s6k and 4E-BP1 were then determined using western blotting. It was found that an eccentric load resulted in a significant increase in p70s6k phosphorylation and reduced 4E-BP1 phosphorylation both in control and suspended rats, but in the case of suspension the response was dramatically reduced. Thus, it can be concluded that a bout of eccentric contractions of isolated rat soleus muscle during functional unloading causes a weaker activation of the Akt-mTORC1-p70s6k signaling pathway compared with the control. This may indicate that it is important to maintain muscle tone for a more efficient muscle perception of an external mechanical signal and subsequent activation of anabolic signaling pathways.

A gender analysis has been carried out to analyze changes in intracellular signaling pathways that lead to the development of chronic alcoholic myopathy. It is known that acute or chronic alcohol intoxication can result in alcohol-induced lesions in skeletal muscles. Chronic alcoholic myopathy occurs much more frequently and can develop either independently or in combination with other forms of alcoholic disease (liver and heart lesions, malabsorption syndrome, or alcohol polyneuropathy). This disease is manifested by atrophy of skeletal muscles and a performance decrement. Most of the studies on the pathogenesis of chronic alcoholic myopathy have been carried out on male patients. Studies on alcoholic myopathy-induced muscle damage in females have not been previously reported.

The electrical resistivity of tissues, organs, and body segments of reptiles (grass snakes) during experimental cooling has been studied for the first time. The observed significant decrease in the phase angle recorded in a tail segment and the significant decrease in the electrical resistivity of the liver and lung during body cooling are associated with the blood-flow redistribution from the tail to the mid-body, liver, and lungs.