卷 64, 编号 5 (2019)

Abstract—The hypothesis that formed the basis of this work has been made on our studies that have shown that giant multi-domain muscle proteins of the titin family (titin isoforms and myosin-binding protein C paralogs) form amyloid aggregates in vitro. We have identified a number of features of the amyloid aggregation of the above-mentioned proteins using a number of methods, including X-ray diffraction: (1) the ability to aggregate under reduced ionic strength at pH 7.0; (2) a high aggregation rate; (3) the formation of aggregates that have a quaternary structure like the cross-β structure, which is characteristic of many amyloids; (4) the absence of changes in the secondary structure in the formation of amyloid-like aggregates; and (5) the partial reversibility of amyloid aggregation. In this paper, we raise the following questions. Is amyloid aggregation of these proteins possible in vivo? If so, what could be the functional significance of such aggregation in a muscle cell? We believe that amyloid-like structures can be formed temporarily upon the interaction of individual molecules of multi-domain muscle proteins in the process of muscle contraction in the sarcomere. Such changes would certainly be accompanied an increase in the stiffness of the sarcomeres and the muscle in general, that can play a positive role in preventing harmful effects on the muscle under extreme physical exercise.

Abstract—Changes in the expression of the titin gene and alternative splicing of titin pre-mRNA from exon 50 to exon 111 in rat soleus muscle were analyzed following 3-day functional unloading (the HS group). Using real-time RT-PCR, it was found that the expression level of the titin gene in the rat soleus muscle from the HS group was higher by 1.81 times (p ≤ 0.01, n = 6) than the control level (n = 7). It was shown that all studied exons of titin mRNA are present in rats soleus muscle from the two groups. Our results demonstrate that 3-day functional unloading is accompanied by an increase in the expression of the titin gene in rat soleus without changes in alternative splicing from exon 50 to exon 111.

Abstract—It has been previously shown in the study of the kinetic behavior of cGMP-specific phosphodiesterase in preparations of the outer segments of bovine retinal rods, which was temporarily activated by 2 μM GTP at high and low concentrations of free ions of Ca²⁺ (100 μM and <10 nm, respectively), that the lifetime of cGMP-specific phosphodiesterase in the active state significantly decreased (by ≈2 times) when low concentrations of free calcium ions were used. This suggested that there is a Ca²⁺-binding protein in the outer segments of bovine retinal rods that can interact with the so-called free transducin and regulate the rate of hydrolysis of GTP, which is bound in its active site, depending on the concentration of free Ca²⁺ ions. This paper is devoted to a discussion of the known Ca²⁺-binding proteins that occur in the outer segments of bovine retinal rods that could play the role of a potential regulator.

Abstract—In this study we present a modified method for determination of the antioxidant capacity of biological fluids and tissues based on the use of a chemiluminescent model system in which oxidation of luminol was induced by 2,2'-azobis(2-amidinopropane) dihydrochloride. It was shown that the addition of EDTA as an extra component gives the system a number of advantages. The intensity of chemiluminescence at the stationary stage was increased substantially (by 6–7 times) and stationarity remained unchanged for a long period of time (more than 1 h). As well, it should be noted that no significant increase in the intensity of chemiluminescence occurred in the presence of biological fluids or individual antioxidants (human serum albumin and ascorbic acid) after the end of the latent period but it was observed in the absence of EDTA. Taking the fact into account that the values of the latent periods that were determined while introducing some low-molecular-weight antioxidants (trolox and uric acid) into our system, as well as human biological fluids (blood serum and tear fluid), were not significantly different from those obtained in the system without EDTA, we suppose that EDTA had no impact on luminol oxidation reactions. The proposed system can also be used to evaluate antioxidant capacity of various tissues. The obtained data are discussed in terms of prospects for the use of the proposed modified method for determination of the antioxidant capacity of biological material in clinical practice.

Abstract—Spin labeling EPR spectroscopy was used to study the structural and conformational characteristics of human serum albumin and human erythrocyte membranes under normal conditions and with symptoms of heart failure. 5-Doxyl stearic acid and 16-doxyl stearic acid were used as spin labels, whose paramagnetic NO fragments are bound to different sites of the hydrocarbon chain. The EPR spectra of 16-doxyl stearic acid indicate that in the physiological temperature range serum albumin molecules are characterized by several types of fatty acid binding sites, which differ in parameters of spin-label rotational diffusion. This distribution of fatty-acid binding sites was typical for the blood serum of all patients who participated in our study, regardless of deviations from the normal blood parameters. The microviscosity of erythrocyte membranes from patient blood was measured using both 5-doxyl stearic and 16-doxyl stearic spin labels, whose paramagnetic fragments are located at different depths inside the lipid bilayer. It was found that in patients with an increased erythrocyte distribution width, the membrane lipid microviscosity is statistically significantly higher than under normal conditions.

Abstract—An adjustable algorithm was developed to determine the mean sarcomere length in isolated cardiomyocytes during their active contraction in unloaded or loaded conditions. The algorithm is based on the discrete Fourier transform (DFT) and includes an additional processing of the input signal, that is, the sarcomere striation pattern of the cardiomyocyte, and the amplitude-frequency spectral curve, which is obtained after performing the DFT to determine the sarcomere length with higher precision. The algorithm was shown to be efficient in analyzing the sarcomere striation pattern in isolated cardiac cells.

Abstract—Two methods for studying the functioning of the mitochondrial ATP-sensitive potassium channel, which plays an important role in cell physiology and especially in cardio- and neuroprotection, have been compared. It has been shown that the spectrophotometric method, which is most often used to study this channel and the influence of its modulators, has a number of limitations and mainly provides a qualitative assessment. A modification of this method is proposed, which makes it possible to obtain optical density changes recorded in a linear form that enables quantification of the change in the optical density and, as a consequence, allows a more accurate determination of the effect of various modulators. The concentration of ATP that causes half-maximal inhibition of the rate of potassium transport (ІС_{50_АТP}) in the rat liver mitochondria has been determined by two different methods. The ІС_{50_АТP}, as assessed by direct measurement with a potassium-selective microelectrode under 2,4-dinitrophenol-induced efflux of potassium, was 23 μM; it was 400 μM as assessed by the spectrophotometric method. The data we obtained suggest that recording of the 2,4-dinitrophenol-induced potassium efflux may be a more effective method for evaluating ATP-dependent transport of potassium ions in mitochondria.

Abstract—Different synthetic calcium phosphate compounds are used as osteoplastic materials for filling of bone defects during surgical reconstruction of bone. Synthetic nanosized hydroxyapatite is of particular interest because of its similarity to the chemical composition of bone and its osteoinductive potential. However, it is also known that nanosized hydroxyapatite can inhibit the processes of biointegration of biomaterials, although we have no clear understanding of the mechanisms that are responsible for this effect. In our in vitro studies suppression of cell adhesion on nanosized hydroxyapatite that may lead to anoikis was shown. Studies in which rat subcutaneous heterotopic implantation methods were used showed that nanosized hydroxyapatite in vivo formed a slightly resorbable agglomerate that blocks cell migration into the material, as well as neocollagenesis processes in it, including the processes of encapsulation of the material. In this case, the processes of neocollagenesis along the periphery of the sample were observed only over a dense layer of dead cells (cellular debris) surrounding the agglomerated nanosized hydroxyapatite. Addition of demineralized bone collagen matrix to nanosized hydroxyapatite as a conductive component contributed to colonization of the material by the cells, resorption of nanosized hydroxyapatite, and active construction of the neocollagen matrix. These results show that modification of nanosized hydroxyapatite with a conductive component is required in order to prevent its agglomeration and thus increase its biointegration and osteoinductive potential in the body.

Abstract—Morphogenetic effects of two exogenous sex steroid hormones, testosterone and estradiol, during planarian regeneration have been studied. Anterior regenerants, which retained the head ganglion after cutting, exhibited the highest sensitivity to the introduced hormones. The influence of the studied steroids on the growth rate of their blastema was different: the regeneration process was stimulated by estradiol and inhibited by testosterone. In posterior regenerants, the inhibitory effect of testosterone was also present, while estradiol had hardly any influence on the recovery rate. Both hormones significantly increased mitotic activity in the anterior and posterior regions of the regenerants. The highest mitotic index values were observed in the regions that were most remote from the cutting zone and in those immediately adjacent to it. As a working hypothesis, it is proposed that specific effects of either hormone were related to the formation of specific hormone–receptor complexes and to the pattern of hormone receptor distribution in the proximal and distal regions of the planarian body.

Abstract—Thallium ions were tested for their effect on the spontaneous contraction of the frog heart muscle and rat heart mitochondria. Tl⁺ ions reduced all parameters of spontaneous contractions in heart muscle preparations when used at 1.0, 2.5, and 5 mM in Ringer’s solution. The greatest decreases were observed for the frequency of contractions, as well as the amplitudes, the rate of rise, and the rate of relaxation of twitch-type contractions. When Ca²⁺ was added to mitochondria in the presence of TlNO₃ and NaNO₃, the mitochondrial permeability transition pore (MPTP) opened in the inner mitochondrial membrane (IMM), leading to an increase in mitochondrial swelling, a reduction of the inner membrane potential, and a decrease in respiration rate in State 3 or the 2,4-dinitrophenol (DNP) uncoupling state. ADP and cyclosporine A (CsA) inhibited the Tl⁺ effects. Thus, Tl⁺-stimulated Ca²⁺ entry into cardiomyocytes may induce overloading of heart mitochondria with Ca²⁺ and Na⁺ ions and stimulate the MPTP opening in the IMM. The findings provide additional information on the mechanisms of thallium toxicity in the cardiac muscle in vivo. Tl⁺ ions are undesirable for use in myocardial tests in arrhythmia, heart failure, and especially diastolic dysfunction.

Abstract—The body’s response to stress is mediated by the interaction of catecholamines with adrenergic α- and β-receptors. It has been established that, in contrast to α1- and β-adrenoceptors, α2-adrenoceptors are involved in feedback loops of the simpatoadrenal system, which controls the release of catecholamines (norepinephrine and epinephrine) to save energy resources and the function of peripheral organs under an overload of catecholamines. Violations of the feedback mechanisms lead to various pathologies, including hypertrophic heart remodeling, followed by the development of heart failure. We previously found the expression of α2-adrenoreceptors in the plasma membrane of cardiomyocytes, where they participate in the regulation of the intracellular level of Ca²⁺. We suggested that these receptors are able to locally control the response of the heart muscle to stress in addition to the traditional mechanism. We have shown in this study that sarcolemmal α2-adrenoreceptors attenuate the positive inotropic effect of adrenergic stimulation in papillary muscles by controlling the level of free Ca²⁺ in cytosol. The ability of α2-adrenoreceptor agonists to suppress intracellular spontaneous Ca²⁺ oscillations increases the efficiency of systolic function of papillary muscles and reduces the likelihood of dangerous ventricular arrhythmia. Thus, α2-adrenoreceptors in the sarcolemmal membrane of cardiomyocytes have their own protective potential, which can prevent pathological remodeling of the heart muscle under chronic stress.

Abstract—Rhabdomyolysis is a clinical syndrome caused by damage to skeletal muscles. Its frequent severe complication is acute kidney injury. The nephroprotective potential of melatonin (5 mg/kg) in rhabdomyolysis-induced acute kidney injury has been studied in experiments on mature outbred laboratory white rats. A single administration of 8 mL/kg glycerol induces the oliguric form of acute renal failure, which is accompanied by a reduction in glomerular filtration rate, an increase in plasma creatinine level, hyperkalemia, aciduria, notable proteinuria, and impaired nephron reabsorption function. It has been found that melatonin administration exerts a cytoprotective effect on epithelial cells of renal tubules and considerably limits the extent of the damage, preventing the development of oliguria, retention azotemia, and excessive loss of sodium ions. It reduces proteinuria and increases urine pH. The protective effect is due to the antioxidant ability of melatonin, which prevents the development of oxidative stress in kidneys. These results substantiate the prospects of further studies of the nephroprotective potential of melatonin in kidney disorders of various origins.

Abstract—We have previously demonstrated that hypothermia significantly modulates the effect of ATP on the contractile activities of various types of rodent locomotor muscles. The aim of this study was to compare the effects of ATP on contraction of mouse locomotor (m. soleus) and respiratory (m. Diafragma) muscles at normal and low temperatures. It has been found that a decrease in the ambient temperature to 22°C is associated with a decrease in the force of muscle contraction (m. Diafragma) induced by electrical stimulation and carbachol, as well as with an increase in the contractile force of m. soleus. The potentiating effects of ATP in these muscles are preserved even in response to temperature reduction, but they are enhanced only in carbachol-induced contractions, thus indicating a postsynaptic localization of a thermal sensitive element in purine modulation. The characteristic features of ATP release modulation with the predominant postsynaptic thermal sensitive link in different motor units in hypothermia in mice may underlie the adaptive mechanisms of this small rodent.

Abstract—This paper provides a review of studies on the effects of hypogravity on neuromuscular system function. It is known that exposure to microgravity causes a series of events that occur in the neuromuscular system, leading to the development of so-called “hypogravity motor syndrome.” Despite a large number of publications related to the pathogenesis of the hypogravity motor syndrome, the decrement in motor function is largely attributed to the changes in the morphofunctional characteristics of skeletal muscles. However, based on the information presented in this paper that provides insight into the processes occurring in motor units the under condition of near weightlessness, a synaptic transition also appears to be essential.