Biochemistry (Moscow), Supplement Series A: Membrane and Cell Biology最新文献

A quantitative study of subthreshold excitatory postsynaptic potentials (EPSP) recorded intracellularly in giant premotor interneurons of the terrestrial snail was carried out after the formation of a conditioned defensive reflex of food aversion in snails with increased level of serotonin. The results showed a significant increase in the number of low-amplitude EPSP with an amplitude from 0.3 to 0.5 mV in the giant premotor interneurons of defensive behavior after learning and increasing the level of serotonin. The observed increase in the number of EPSP may indicate either an increase in the number of action potentials in the corresponding presynaptic neurons or an increase in the amplitudes of the EPSP that were previously undetectable.

We have studied the process of electroporation of bilayer lipid membranes (BLMs) made of dioleoylphosphatidylcholine (DOPC). We obtained experimental data on the average lifetime of the membrane as a function of applied transmembrane voltage in the range of 200–375 mV. The analysis of the obtained data showed that the dependence is nonmonotonic and cannot be described in terms of the classical theory of electroporation. These results are consistent with modern models of the process of formation of through conductive pores in a membrane. The above models imply a complex pore energy profile and its dependence on a membrane tension and an external electric field. Thus, we have shown that the classical theory of electroporation does not satisfy the experimentally observed dependencies of the average membrane lifetime on the applied potential difference and requires further refinement.

One of the main stages of the infectious process, which largely determines the course and outcome of the disease, is the primary contact of the pathogen with the host cells. A key role in this interaction of gram-negative bacteria with immunocompetent cells of the macroorganism is played by lipopolysaccharide of the outer membrane, which initiates the launch and development of immune reactions by interacting with a number of specific receptors, primarily CD14 and TLR4. The aim of this study was to quantify by atomic force microscopy the force characteristics of the interaction of Yersinia pestis lipopolysaccharide of the EV vaccine strain with CD14 and TLR4 receptors on the surface of murine J774 macrophages. The lipopolysaccharide was isolated from Y. pestis cells of the EV vaccine strain grown at 27°C. Fluorescence and confocal microscopy were used to evaluate the expression of receptors on the cell surface. Using monoclonal antibodies to CD14 and TLR4 receptors, the force characteristics of the interaction of lipopolysaccharide on the surface of the cantilever probe (tip) with J774 macrophages were evaluated by force spectroscopy. The conditions of immobilization of J774 macrophages on glass made it possible to scan their surface and assess the force of adhesion to the cells of target antigens by atomic force microscopy. Incubation of immobilized macrophages in solutions with monoclonal antibodies to CD14 and TLR4 receptors caused a decrease in the main force characteristics of interaction in the J774 macrophage–Y. pestis lipopolysaccharide system compared with intact, untreated cells. A similar effect was observed after pretreatment of cells with a solution of the same lipopolysaccharide without monoclonal antibodies. The results obtained indicate the ability of the lipopolysaccharide chemically bound to the probe to interact with CD14 and TLR4 receptors on the surface of macrophages.

The effect of exogenous auxin on changes in the fatty acid composition of the total lipids of leaves and roots of spring wheat (Triticum aestivum L.) seedlings was studied. It was found that the diversity of fatty acids in vegetative organs (leaf and root) depended not only on the concentration of auxin, but also on the donor of nitric oxide (N₂ and NO₃). With an increase in the concentration of exogenous auxin, there was an increase in microviscosity and a decrease in the permeability of membranes of vegetative organs of wheat, which was confirmed by a decrease in the double bond index (DBI). At the same time, there was an increase in the concentration of saturated fatty acids (palmitic and stearic), which were used as precursors for the formation of very long-chain fatty acids (VLCFA). It was found that exogenous auxin led to an increase in the total content of VLCFA in leaves with a deficit (8.4%) and an excess of NO donors (12.3%). The introduction of exogenous auxin eliminated significant differences in desaturase activity in wheat roots at different levels of nitric oxide donors. It was suggested that the biosynthesis of docosadienoic acid (C_22:2) in leaves is one of the key stages in the formation of the adaptive response of cell membranes to the effects of abiotic stresses during plant ontogenesis. An increase in the NO level promoted the movement of auxin from the roots to the shoots, which can serve as a regulator of the activity of elongases and desaturases during the synthesis of VLCFA.

The activator of the large-conductance Ca²⁺-activated K⁺ channel (BK_Ca) NS1619 is known to have a pleiotropic action and is able to affect the functioning of other transport systems of the cell and its organelles. In this work, we have studied the effect of this benzimidazole derivative on the functioning of isolated mouse skeletal muscle mitochondria. NS1619 has been shown to dose-dependently inhibit respiration and oxidative phosphorylation of mouse skeletal muscle mitochondria fuelled by glutamate/malate (complex I substrates) or succinate (complex II substrate). This action of NS1619 is based on the inhibition of the activity of complexes I, III, and IV of the respiratory chain of organelles, as well as ATP synthase and is accompanied by a dose-dependent decrease in the membrane potential of organelles fuelled by the above substrates or ATP. In addition, NS1619 significantly reduces the ability of mitochondria to uptake and retain calcium ions in the matrix. At the same time, we noted the antioxidant effect of NS1619 expressed in a decrease in the production of hydrogen peroxide by skeletal muscle mitochondria fuelled by glutamate and malate. The mechanisms of the possible toxic effects of NS1619 on skeletal muscle mitochondrial function and its contribution to the side effects observed in the treatment of muscle pathologies in vivo are discussed.

The processes of electronic transport in chloroplasts of two contrasting species of Tradescantia, the shade-tolerant species Tradescantia fluminensis and the light loving species T. sillamontana, grown in moderate or strong light conditions were investigated. The parameters of fast (OJIP test) and slow induction of fluorescence (SIF) of chlorophyll a in chloroplasts in vivo and in situ were used as indicators reflecting the photochemical activity of photosystem 2 (PS2). The coefficient of nonphotochemical quenching of chlorophyll a fluorescence, which provides protection of the photosynthetic apparatus from light stress, was determined from the SIF kinetics. The functioning of photosystem 1 (PS1) was monitored by the kinetics of photoinduced changes in the redox state of P₇₀₀, the reaction center of PS1, recorded by electron paramagnetic resonance. A significant difference in the dynamics of changes in photosynthetic parameters of shade-tolerant and light loving tradescantia species under conditions of prolonged acclimation of plants (up to 5 months) to moderate (50–125 µmol photons m^–2 s^–1) or strong (850–1000 µmol photons m^–2 s^–1) illumination with photosynthetically active white light was observed. In the light loving species T. sillamontana, photosynthetic parameters of chloroplasts changed slightly during acclimation of plants to moderate and strong light. Photosynthetic characteristics of leaves of shade-tolerant species T. fluminenesis were sensitive to the conditions of illumination, which indicated a weakening of photochemical activity with an increase in light intensity during acclimation of plants. The effect of attenuation of photosynthetic parameters of the leaves was reversible, that is, the fluorescence parameters returned to the initial level after attenuation of light.

One of the key receptors on the surface of platelets, non-nuclear cells responsible for preventing blood loss when blood vessels are damaged, is the receptor for the extracellular matrix protein collagen, glycoprotein VI (GPVI). GPVI triggers tyrosine kinase signaling in platelets, simultaneously initiating calcium signaling via phospholipase Cγ2 (PLCγ2) and phosphoinositide signaling via phosphoinositide-3-kinase (PI3K). Previously, our group demonstrated that among healthy donors there is more than a twofold variability in calcium response to activation through the GPVI receptor. Here, a computer model of platelet activation through the GPVI receptor is proposed to explain this phenomenon. This model is a system of ordinary differential equations integrated with the LSODA method. The model equations were derived from our previously published model of platelet activation via the CLEC-2 receptor. Using the developed model, a monotonic dependence of the degree of platelet activation on the number of GPVI receptors was predicted. An analysis of the sensitivity of the model to its parameters showed that the platelet response to activation through GPVI is determined by the number of GPVI receptors, as well as the catalytic parameters of tyrosine kinases, while a twofold change in the number of receptors is sufficient to explain the observed phenomenon. Thus, it was theoretically predicted that the variability of calcium responses of platelets to their stimulation through the GPVI receptor could be determined by the variability in the number of GPVI receptors on the platelet surface of healthy donors.

Stimulation of mitochondrial respiration in state 4 without changes in passive proton leakage is known to be accompanied by a decrease in the H⁺/O ratio. In the present work, it was found that during the oxidation of succinate by liver mitochondria, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and α,ω-hexadecanedioic acid (HDA) effectively stimulate respiration in state 4, and their action is, unlike the protonophore uncoupler DNP, is not caused by an increase in the proton conductivity of the inner membrane. Under these conditions, TMPD and HDA do not significantly affect the efficiency of oxidative ATP synthesis and energy transformation by complex IV (cytochrome c oxidase). The data obtained are considered as evidence that during the oxidation of succinate by liver mitochondria, TMPD and HDA selectively switch off ETC complex III from energy transformation. It is theoretically substantiated that, under these conditions, the H⁺/O ratio can be determined based on the ratio of respiratory rates in the absence and presence of TMPD and HDA. Based on this model, we considered the change in the H⁺/O ratio depending on the stimulation of mitochondrial respiration in state 4 by TMPD and HDA. It has been established that under the influence of TMPD or HDA, the value of the H⁺/O ratio decreases during the oxidation of succinate from 6 to the limiting values of 2. We conclude that in liver mitochondria during free respiration, in contrast to the oxidative ATP synthesis, the values of the H⁺/O ratio are 4 and 2 for complexes III and IV, respectively.