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S N Udal'tsov

Publications and source records attributed to S N Udal'tsov.

18 recordsLinked to original sources
PubMed2005

The structure of mixed synapses in Mauthner neurons during exposure to substances altering gap junction conductivity.

The aim of the present work was to study the effects of dopamine, ecdysone, and chlorpromazine, substances which alter the conductivity of gap junctions (GJ), on the ultrastructure of mixed synapses in goldfish Mauthner neurons. These studies showed that dopamine, which increased the electrical conductivity of mixed synapses, appeared to target desmosome-like contacts (DLC). Hypertrophy of DLC, along with increases in the numbers of bridges within their clefts, showed that the mechanism by which dopamine increased electrical conductivity involved neuronal actin. This was indicated by the transformation of isolated monomeric muscle actin into polymerized actin in the presence of dopamine. Conversely, GJ were degraded by dopamine. Ecdysone, which also increased GJ conductivity, altered GJ structure, increasing the numbers of GJ at the attachment zone and decreasing the sectional length. but had virtually no effect on DLC structure. Ecdysone also showed no interaction with DLC in in vitro conditions. The mechanism of action of ecdysone is thus associated primarily with GJ function. Chlorpromazine, which decreased GJ conductivity, partially or completely degraded the fibrillar juxtamembrane material of DLC, preventing actin polymerization, with corresponding in vitro effects, but produced no changes in GJ. The mechanism of its action therefore appears to be based on changes in the state of neuronal actin.

Animals↗
PubMed2004

Morphofunctional changes in incubated Mauthner neurons in goldfish treated with peptides from scorpion venom.

Electron microscopy with negative contrast showed that direct interaction of one of the peptide fractions of scorpion venom with monomeric chromatographically pure actin led to polymerization of actin, transforming it from the globular form to the fibrillar form. The effects of prolonged orthodromic stimulation on the evoked electrical activity and ultrastructure of Mauthner neurons (MN) were studied in incubated slices of goldfish medulla oblongata in the presence of this actin-polymerizing venom fraction. Peptides in this fraction were found to stabilize the amplitude of the electrical response of MN to exhaustion and to protect the ultrastructure of afferent chemical synapses and the neurons themselves from damage induced by stimulation. Enhancements in morphofunctional resistance were accompanied by stabilization of actin-containing specialized synaptic structures--desmosome-like contacts. The data obtained here provide evidence that peptides of this fraction of scorpion venom have direct actions on the actin component of the MN cytoskeleton and demonstrate potential for its use as a pharmacological tool able to penetrate living cells with value for studying the role of actin in the mechanisms of adaptation and memory.

Animals↗
PubMed2004

[Substances affecting gap junction conductivity and Mauthner neuron mixed synapses].

The aim of this work was to study the effect of dopamine, 20-hydroxyecdysone and chlorpromazine, drugs changing the conductance of gap junctions (GJs), on the ultrastructure of goldfish Mauthner neurons mixed synapses. It was shown that desmosome-like contacts (DLCs) were the presumable targets for dopamine, that increased the electrotonic conductance of mixed synapses. Their hypertrophy, as well as an increase in the number of bridges in their clefts suggests that neuronal actin is involved in the mechanism of dopamine-induced increase of electrotonic conductance. This assumption is further supported by the transformation of extracted monomeric muscular actin into polymeric actin in the presence of dopamine. On the contrary, GJs were shown to be damaged by dopamine treatment. Ecdysone, which is also known to increase the conductance of GJs, changed their structure, increasing their number in the zone of apposition and reducing the profile length, but practically not affecting the DLC structure. It also does not interact with isolated actin in vitro. Therefore, the mechanism of ecdysone action is mainly associated with GJ function. Chlorpromazine, which reduces the conductance of GJs, was shown to damage, partially or completely, DLC admembranous fibrillar material, thus preventing actin polymerization, as shown by in vitro experiments, but had no effect on GJs. Therefore, the mechanism of its action, appears to be based on the changes in the state of neuronal actin.

Actins↗
PubMed2003

[Effect of polypeptides from scorpion venom on morpho-functional changes of the incubated Mauthner neurons in goldfish].

Using the electron microscopical method of negative staining it was shown that one of the fractions obtained from scorpion venom directly interacts with monomeric chromatographically pure actin causing its polymerization and transformation from globular into fibrillar form. The effect of long-term orthodromic stimulation on evoked electric activity and on the ultrastructure of Mauthner neurons (MN) in the goldfish hindbrain slices incubated in vitro was studied after the application of this venom fraction. The peptides of this fraction were shown to stabilize the amplitude of MN evoked electric responses to fatigue and to protect the ultrastructure of afferent chemical synapses and MN themselves from stimulation-induced injuries. Increase in morpho-functional resistivity is accompanied by the stabilization of specialized synaptic structures--actin-containing desmosome-like junctions. These data suggest the direct effect of peptides from scorpion venom fraction on actin component of MN cytoskeleton and show the perspective for their application as pharmacological tools capable of penetration into the living cells that may be used for investigation of the role of actin in the mechanisms of adaptation and memory.

Actins↗
PubMed1986

[Detection of giant axospinal synapses in the hippocampus on semithin sections].

A histological study of plastic semithin hippocampal sections after the treatment of myosin with tannic acid and detergent and then with subfragment-1 has shown the neuronal dendrites to be covered with dark spine-like thickenings. Electron microscopic analysis of the same preparations has revealed that the electron dense discrete formations represent synaptic terminals, situated on the dendrites with a definite periodicity. We discuss the use of such a method for the quantitative calculation of synapses in nerve tissue at the combined histological and electron microscopic levels of investigation.

Animals↗
PubMed1986

[Cytochemical detection of actin in the structure of the synaptic apparatus of hippocampal field CA3].

Ultrastructural distribution of actin in dendrites, dendritic spines and presynaptic boutons of the hippocampal area CA3 of the guinea pig was investigated using decoration and immunocytochemical methods. The distribution of actin was non-homogeneous in all the parts of neurons. The highest concentration of this contractile protein was revealed in the spine cytoplasm. Here actin forms a dense cytoskeleton meshwork and is present also in postsynaptic densities. An intimate interaction between the spine actin cytoskeleton and the postsynaptic actin densities has been revealed. This feature may indicate the involvement of actin cytoskeleton in the organization and maintenance of dimensions, location and geometry of active zones.

Actins↗
PubMedDate not supplied

[Absence of seasonal adaptive changes in the isoformic state and functional properties of actin-containing and thin filament proteins in skeletal muscles of hibernating squirrels].

The data indicating the absence of seasonal changes in the isoform composition and functional properties of actin and thin filament associated proteins from skeletal muscles of hibernating ground squirrels were obtained. Taking into account the data obtained earlier by the authors on significant qualitative and quantitative changes in isoform composition and functional properties of the other contractile protein, myosin, it is concluded that the suppression of contractile capacity of the executive apparatus of skeletal muscles of animals upon hibernation and its repair upon arousal are determined by the above adaptive changes in myosin.

Actins↗
PubMedDate not supplied

[Changes in composition of cardiac myosin light chains in dilated cardiomyopathy: effect on functional properties].

A reduction (by 16-24%) in the amount of myosin regulatory light chains (LC2) in all heart sections of patients with dilated cardiomyopathy was found. The appearance of atrial essential light chains in ventricular myosin (up to 23%) not typical for this heart section in norm was also revealed. The decrease in LC2 content leads to a considerable inhibition of actin-activated ATPase activity and a loss of Ca2+ sensitivity of reconstructed filaments of myosin isolated from atria and ventricles of patients with dilated cardiomyopathy. The hybridization of myosin molecules from heavy chains of pathological human left ventricular myosin and light chains of pig left ventricular myosin leads to an increase in actin-activated ATPase activity of myosin and its Ca2+ sensitivity to the control level. The data suggest strongly the contribution of LC2-deficit to the distortion of functional properties of myosin in dilated cardiomyopathy. In contrast, the appearance of atrial LC1 in ventricle in dilated cardiomyopathy is a factor improving these properties.

Actins↗
PubMedDate not supplied

[Properties of C protein from skeletal and cardiac muscles of the ground squirrel Citellus undulatus at various stages of hibernation].

Changes in the molecular weight and functional properties of the C and X proteins from skeletal muscles and the C protein from the cardiac muscle of hibernating ground squirrels Citellus undulatus at different stages of the hibernation were studied. A decrease in the molecular weight of the C protein from fast fibers of skeletal muscles of hibernating ground squirrels compared with awakening and active animals was revealed. The appearance of shorter molecules of the C protein upon hibernation was accompanied by a lowering of its capacity to enhance the actin-activated ATPase activity of control myosin and by the inhibition of its Ca(2+)-sensitivity. No similar changes were observed for the skeletal X protein and the cardiac C protein. The influence of the skeletal C protein on the main functional properties of myosin allows one to draw a conclusion about its contribution to the inhibition of contractile activity of skeletal muscles upon hibernation. The physiological significance of the changes in the C protein upon hibernation is discussed in connection with similar changes in some cardiomyopathies.

Actomyosin↗
PubMedDate not supplied

[Human soleus fibers contractile characteristics and sarcomeric cytoskeletal proteins after gravitational unloading. Contribution of support stimulus].

The effects of support withdrawal and support stimulation on the contractile characteristics of human soleus fibers and cellular factors which influence them were studied. The experimental model of the "dry" head-out water immersion was used in the study. In this model, the hydrostatic pressure on different sites of the body surface are equal so that the experimental conditions are close to the complete supportlessness. A 7-day exposure to dry immersion resulted in a decrease in the maximal isometric tension of the skinned fibers, a decline in the myofibrillar Ca2+-sensitivity, and the relative loss of the titin and nebulin content. A significant decrease in the percentage of fibers containing slow myosin heavy chains was also observed after dry immersion. The application of the mechanical stimulator influencing the plantar support zones with a pressure of 0.2 +/- 0.15 kg/cm2 6 times a day for 20 minutes of each hour brought about a complete prevention of the above listed effects of dry immersion. The data obtained allow one to conclude that the decline in maximal tension and Ca2+-sensitivity as well as myosin shift and loss of sarcomeric cytoskeletal proteins are associated with the support withdrawal during the exposure to dry immersion.

Cytoskeletal Proteins↗
PubMedDate not supplied

[Myosin light chains of skeletal and cardiac muscles of ground squirrel Citillus undulatus in different periods of hibernation].

The isoform composition of myosin light chains and the extent of their phosphorylation in skeletal and cardiac muscles of ground squirrel Citellus undulatus in different periods of hibernation were studied. Regulatory myosin light chains of skeletal muscles of hibernating ground squirrels were completely dephosphorylated, while 25% of these light chains in active animals were phosphorylated. During hibernation, a shift of isoform composition of essential and regulatory skeletal muscle myosin light chains toward slower isoforms was observed, which is evidenced by the data obtained on m. psoas and on the totality of all skeletal muscles. In the atrial myocardium of hibernating ground squirrels, ventricular myosin light chains 1 (up to 60%) were registered. In contrast, during arousal of ground squirrels, in ventricular myocardium the appearance of atrial myosin light chains 1 (up to 30%) was revealed. A possible role of posttranslation changes in myosin light chains and their isoform shifts in the hibernation scenario is discussed.

Animals↗
PubMedDate not supplied

[Binding of F-protein (phosphofructokinase) to F-actin].

By the use of sedimentation method the interaction of F-protein (phosphofructokinase) with F-actin has been studied in 0.1 M KCl, 10 mM K-phosphate buffer, pH 6.5. The calculated value of the constant of F-protein binding to F-actin is (7.3 +/- 1.0) X 10(5) M-1. The number of the F-protein binding sites calculated per chain weight of 80,000 is 0.43. The binding of F-protein to F-actin was found to be affected by pH-value.

Actins↗
PubMedDate not supplied

["Freezing" of the conformation of thin filaments in a single skinned fiber of the rabbit muscle by glutaraldehyde].

It is shown that short treatment of a single skinned rigor fibre from rabbit m X psoas with 0.05% glutaraldehyde in the absence of Ca ions leads to a modified state of the contractile apparatus. After the addition of 5 mM MgATP in the absence of Ca ions to the fibre a sharp rise and subsequent slow decay of tension were observed in contrast to the tension drop in case of the control (unmodified) specimen. The tension transients following quick stretch (L 0.5%) were similar to those for Ca-activated tension. In case of the modified relaxed fibre such a phenomenon was not observed. These results can be explained by "freezing" with glutaraldehyde the thin filament structure either in the "on" or "off" states. The relation of these results to the cooperativity in the regulation mechanism of contraction is discussed.

Actins↗
PubMedDate not supplied

[Structural changes in actin filaments during binding with phosphofructokinase (F-protein), detected using an optical diffraction method].

It has been previously shown by us that phosphofructokinase (F-protein) binds to rabbit skeletal muscle F-actin and reconstituted thin filaments forming ordered bundles. Upon low molar ratios of phosphofructokinase to actin in the complex bundles the enzyme molecules are arranged between actin filaments regularly in the form of crossbridges. The increase of phosphofructokinase: actin ratio up to equimolar one and more leads to the filling of the space between actin filaments with phosphofructokinase-molecules. In these bundles the inclined cross striation with axial repeat of about 7.0 nm is clearly seen. Optical diffraction analysis of the micrographs revealed new features in the structure of such complexes in comparison with F-actin and reconstituted thin filaments. Optical diffraction patterns from F-actin and reconstituted thin filaments exhibit the first (35.5 nm) and sixth (5.9 nm) layer lines typical of F-actin helix structure. On the optical diffraction patterns from the complex bundles the meridional reflection of about 7.2nm is present, that is not observed on the optical diffraction patterns from F-actin alone. This reflection is characteristic of optical diffraction- and X-ray patterns of myosin filaments and is the sixth order of axial period of their structure (42.9 nm/6). The structural changes occurring upon binding is supposed to be important for the mutual regulation of functional activity of enzymes and actin-containing filaments in muscle.

Actins↗
PubMedDate not supplied

[Changes in structural organization of reorganized myosin filaments from skeletal muscles of the winter-hibernating suslik Citellus undulatus during awakening].

Electron microscopic observations of myosins, isolated from skeletal muscles of ground squirrels at the different states (hybernation-Mhyb; winter activity--M(act); the beginning of arousal-M(begin); the end of arousal-M(end)) have revealed the differences in the structure of their filaments. The filaments reconstituted from Mhyb, M(act) and M(end) (rectal temperature 27 degrees C) exhibit the ordered structure with the myosin heads arranged regularly (period of 14.3 nm) on the filament surface. The filaments of M(begin) (rectal temperature 12 degrees C) have irregular structure with random arrangement of the myosin head clusters alternating with regions of different length devoid of heads. To elucidate the molecular bases of the structural differences observed by us the solubility of the above myosins, the paracrystal structure of corresponding light meromyosins as well as the composition and state of myosin light chains have been studied. M(begin) appeared to have the greatest solubility in comparison with the other ones. This points to the possible changes in myosin heavy chains during hybernation and arousal although no differences have been revealed in paracrystals of light meromyosins. The amount of light chains (LC3) decreased up to 40% in Mhyb in comparison with Mact and then increased up to 60-70% in Mbegin within 1-1.5 hours of arousal. It is supposed that the rapid changes in isoforms of heavy and light chains in Mbegin lead to disturbance of regular mode of filament assembly in vitro, and can result in the lowering of muscle contraction efficiency and in the increasing of the heat release. The later can contribute to thermogenesis of the animal during arousal.

Animals↗
PubMedDate not supplied

[Seasonal changes in the composition and functions of myosin filaments of the skeletal muscles of ground squirrels Citellus undulatus during hibernation].

The ability of hibernating and arousing ground squirrels' myosins to bind the key enzyme of glycolysis was found to be significantly lower than that of active animals. The findings suggest considerable changes in the myosin heavy and light chain composition occurring during hibernation, as well as a major contribution of the myosin in inhibiting the contractile ability of the skeletal muscles during hibernation.

Adaptation, Physiological↗