Biophysics最新文献

The stability of the binuclear form of dinitrosyl iron complexes with various thiol-containing ligands, such as glutathione, L-cysteine, N-acetyl-L-cysteine, mercaptoethanol, and mercaptosuccinate, has been compared based on the results of exposure of these complexes in an aqueous medium at pH 1.0–2.0, leading to their decomposition as a result of protonation of the thiol group of thiol-containing ligands with the release from the complexes of nitrogen oxide (NO) and nitrosonium (NO+) cations. Complexes with L-cysteine and mercaptosuccinate turned out to be the least stable, they decomposed in acidic solutions at room temperature, whereas the more stable complexes with N-acetyl-L-cysteine, mercaptoethanol, and glutathione decomposed when their solutions were heated at 70–80°C. The decomposition of all these complexes under these conditions occurred within a few min with a concentration ratio of free (not included in the complexes) thiols and the complexes themselves of no more than 1 : 2. With an increase in this ratio, the decomposition time of the complexes increased symbatically with the level of free thiols. The mononuclear form of the thiosulfate complexes decomposed at a thiosulfate/complex concentration ratio of 2 for several min in an aqueous solution at neutral pH. Based on the results obtained, it is assumed that binuclear dinitrosyl iron complexes with L-cysteine can act as the most effective exogenous NO and NO+ donors in experiments on living organisms.

The work is devoted to the mathematical analysis of alternative electron transport pathways in chloroplasts related to the functioning of ferredoxin molecules located at the “crossroad” of electron transport pathways on the acceptor side of photosystem I. This study is based on the kinetic model we proposed earlier, which describes the light-induced transformations of the reaction centers of photosystem I and photosystem II, ferredoxin, plastoquinone, and plastocyanin molecules, as well as the processes of trans-thylakoid proton transfer and ATP synthesis. The effect of alternative channels of electron outflow from ferredoxin molecules (reduction of molecular oxygen, cyclic electron transport around photosystem I, and reduction of thioredoxin) on the dynamics of light-induced redox transformations of electron transport chain transporters has been studied. It has been shown that accelerated electron outflow from photosystem I contributes to an increase in the efficiency of the centers of photosystem I, which is especially important at the initial stages of chloroplast illumination when the Calvin–Benson cycle is inactive. Alternative electron fluxes make it possible to maintain a sufficiently high trans-thylakoid pH difference (ΔрН ≈ 1.8), ensuring efficient synthesis of ATP. The results obtained are compared with experimental data in the context of pH-dependent mechanisms of regulation of electron transport and energy metabolism processes associated with the synthesis of ATP in chloroplasts.

A comparative study of the electrophysiological characteristics of pyramidal (PC) neurons of the dorsal and ventral parts of the CA1 region of the hippocampus of mice was conducted using the patch-clamp method in the “whole cell” configuration. The potassium load was used as a parameter for cell type discrimination (an increase in [K+]o from 3.0 to 8.5 mM in the medium). It has been established that two types of cells with different sensitivities to potassium are found in both parts of the CA1 region. In PC-A type cells, the burst activity caused by a step of current I (from 10 to 200 pA) is potentiated by potassium with an increase in [K+]o to 8.5 mM, whereas in PC-I type cells at currents I < 100 pA there is no effect of potassium loading and at currents ≥125 pA suppression of burst activity is observed. The ratios of the number of PC-A/PC-I cells in the ventral and dorsal regions are 16 : 5 and 8 : 8, respectively. Potassium potentiation of burst activity is higher in ventral PC-A cells than in dorsal cells. The threshold current (Ith) decreases by 2.5 times and a spontaneous burst (pacemaker) activity is manifested only in PC-A cells with potassium loading. The Sag potential and the adaptation index of induced impulse activity are higher in the ventral PC-A cells than in the dorsal cells. The potassium load reduces the Sag potential. An analysis of the voltage characteristics shows that incoming and outgoing (predominantly) slow potassium currents are activated under a potassium load. The currents in the ventral neurons of both types are 1.5–2.0 times lower than in the dorsal neurons (at –100 and +20 mV). Taken together, these data suggest that ({text{K}}_{{text{o}}}^{ + })-sensitive ventral PC-A cells can play an important role in hyperexcitation of neural networks and induction of epileptogenesis.

The effect of 24 h exposure to ethanol at concentrations of 50 and 100 mM on the proliferative, migration, and contractile activity of thoracic aortic smooth muscle cells of rats of three age groups was studied, the early neonatal period of development (1-week-old rats), puberty (5-month-old rats), and the initial period of aging (one-year-old rats). Real-time PCR was used to evaluate the proliferative activity of smooth muscle cells by comparing the relative amount of genomic DNA between control and experiment; wound healing assay was used to determine the migration activity of smooth muscle cells; and a method for assessing the degree of compression of collagen gel was used to determine the level of contractile activity of cells. Ethanol at a concentration of 50 mM did not change the studied properties of aortic smooth muscle cells of rats of all age groups. In the presence of ethanol at a concentration of 100 mM, the following effects were observed: an increase of ~38% (p < 0.01) in proliferative and a decrease of ~12% (p < 0.01) in contractile activity of smooth muscle cells of the aorta of rats of the early neonatal period, as well as a decrease in contractile activity (by ~7%, p < 0.01) and proliferative activity (by ~21%, p < 0.01) of cells of 5-month-old and one-year-old rats. It can be concluded that ethanol at a concentration of 100 mM has different effects on the studied rat cells depending on the age group of animals, and the smooth muscle cells of the aorta of rats in the early neonatal period of development are more sensitive to the effects of ethanol.

The effect of the Thr–Ser–Lys–Tyr peptide isolated from the brain of the obligate hibernating long-tailed ground squirrel Urocitellus undulatus (formerly Citellus undulatus, Spermophilus undulatus) on the polymerization/depolymerization of actin in vitro was studied by electron microscopy. Upon incubation of the peptide with globular (monomeric) actin at concentrations of 0.1 mg/mL (at a ratio of 1 : 1), the formation of single filaments of actin was observed. When the peptide was added to the formed actin filaments, no effects were observed, in particular, actin depolymerization. The possible involvement of the peptide in the polymerization of actin in vivo and a possible contribution to the restoration of the functional activity of the central nervous system after the hibernating animal leaves the state of hypothermia are discussed.

This review analyzes the hypothesis of the retained abilities of various specialized mammalian cells to protect themselves from lethal damage by reactivating the protective atavistic mechanism of cellular plasticity. The development of such protection is accompanied by the transition of differentiated cells from an oxygen-dependent to an oxygen-independent type of metabolism. This transition increases the threshold of cell resistance to death under cancer-inducing damaging effects. At the same time, the level of cell differentiation decreases and embryonic markers appear. Such immature cells are necessary for the regeneration of damaged tissues. However, the regeneration programs of the embryo and the adult body differ significantly. As a result, the process of cellular redifferentiation would be forced to develop not in embryonic conditions but in “nonhealing wound” conditions, in which increases the risk of cancer initiation.

Intracellular accumulation of chemotherapeutic drugs in resistant cells of acute myeloid leukemia cultured in a three-dimensional high-density culture was studied. It was shown that neither the dense arrangement of cells nor the presence of the main ABC family transporter proteins most likely affects the increase in drug resistance of acute myeloid leukemia cells in a three-dimensional high-density cell culture. These data indicate the involvement of other mechanisms in increasing drug resistance in three-dimensional high-density cell cultures of acute myeloid leukemia.

Mobile genetic elements (transposons) demonstrate increased activity in cancer cells. One possible anticancer strategy is the use of the energy costs associated with abnormal activity of mobile elements to create conditions of energy starvation in the cell and the associated launch of the cell death program. A stochastic model of the energy balance in the cell population is proposed in this work, taking the energy costs of retrotransposition of mobile elements LINE-1 and SINE into account. The parameter values in the model were obtained from literature data and new experimental measurements of the ATP level in MCF-7 cells under normal conditions and under hypomethylation conditions. As a result of numerical stochastic modeling, distributions of the variables in the model were constructed, representing the numbers of mRNA molecules and proteins involved in the main energy-consuming cellular processes, as well as the number of active LINE-1 and SINE retrotransposons in the genome. The distributions of energy expenditures by major cellular processes under steady-state conditions were calculated. It is shown that low energy expenditures associated with retrotransposition of mobile elements under normal conditions increase significantly when the model parameters are perturbed. These results can be used to implement practical scenarios of influence on the energy-mediated initiation of cell death programs in cancer cells through the activation of mobile elements.

Cholesterol plays an important role in the structural organization and functioning of spermatozoa membranes. The purpose of this work is to study the structural changes in human spermatozoa membranes using spin probes after removing cholesterol from them using beta-methylcyclodextrin, which binds cholesterol. Using a model system (liposomes with different cholesterol content), it was shown that the presence of cholesterol in liposomes affected the EPR spectra of the spin probe 5-doxyl stearate dissolved in the lipid bilayer, causing an increase in the microviscosity of the membrane. A study performed on human spermatozoa showed that the extraction of cholesterol from them using beta-methylcyclodextrin was accompanied by an increase in the mobility of the spin probe 5-doxyl stearate, indicating that the removal of cholesterol helps to reduce the microviscosity of the lipid bilayer of spermatozoa membranes.

The genotoxicity of sodium nitroprusside on human MCF-7 mammary gland adenocarcinoma cells was studied using the neutral comet method and the contribution of the nitrosonium ion (NO+) to the genotoxicity of sodium nitroprusside was determined. Genotoxicity was assessed by the yield of double-stranded DNA breaks after incubation of a cell culture with the agent for 1.5 hours. The genotoxicity of NO+ in sodium nitroprusside was determined after the procedure of reducing sodium nitroprusside using sodium dithionite, which converts nitroprusside from an NO+ donor to an NO only donor. It has been shown that sodium nitroprusside induces double-stranded DNA breaks in MCF-7 cells after 1.5 hours. This ability does not depend on the stage of the cell cycle: the proportions of damaged cells in the G0/G1 and G2/M+S stages are 29 ± 7 and 27 ± 6%, respectively. As a result of 90-minute incubation with 100 μM of sodium nitroprusside the proportion of cells that were severely damaged in the form of double-stranded DNA breaks is 25–30%, which is close to the proportion of nonviable cells according to the results of the MTT test at 24 and 48 hours of incubation (22 ± 4%). Sodium dithionite, by removing the toxic effect of NO+, protected MCF-7 cells from the genotoxic effects of nitroprusside, which indicates the involvement of NO+ in the formation of double-strand breaks. The mechanisms of double-stranded DNA fragmentation in cells under the action of nitroprusside are discussed.