[Role of light chains of myosin in the regulation of contraction of vertebrate striated muscles].

The data of the study on Ca2+ sensitivity of ATPase activity of myosin from vertebrate striated muscles in the presence of actin and the conditions of its manifestation and disappearance are presented. The role of Ca2+ sensitivity of actin-activated myosin ATPase in the regulation of contraction of vertebrate striated muscles is discussed.

[Seasonal changes in phosphorylation of myosin regulatory light chains and C-protein in myocardium of hibernating ground squirrel Citellus undulatus].

A comparative study concerning the extent of phosphorylation of myosin regulatory light chains and C-protein from the left ventricle of hibernating ground squirrel Citellus undulatus during the periods of hibernation and activity was carried out. During hibernation, regulatory light chains of ground squirrel were found to be completely dephosphorylated. In active animals, the share of phosphorylated light chains averages 40-45% of their total amount. The extent of phosphorylation of the cardiac C-protein during hibernation is about two times higher than that in the active state. Seasonal differences in phosphorylation of the two proteins of ground squirrel myocardium are discussed in the context of adaptation to hibernation.

[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.

Comparative electron microscopic study on projectin and titin binding to F-actin.

Using the system of F-actin paracrystals, we have obtained electron microscopic evidence that projectin from synchronous flight muscles of Locusta migratoria binds to actin filaments in the same fashion as skeletal titin. Control actin paracrystals formed in the presence of Mg(2+) ions have great width and length and blunted ends. The addition of either projectin or titin results in disruption of compact ordered packing of F-actin in paracrystals and leads to the formation of loose filament bundles with smaller diameters and tapered ends. It is also accompanied with the appearance of individual actin filaments in considerable amounts. The effect becomes more pronounced with the increase in concentrations of added projectin or titin. Possible physiological implications of projectin-actin interactions are discussed.

Order-disorder structural transitions in synthetic filaments of fast and slow skeletal muscle myosins under relaxing and activating conditions.

In the previous study (Podlubnaya et al., 1999, J. Struc. Biol. 127, 1-15) Ca2+-induced reversible structural transitions in synthetic filaments of pure fast skeletal and cardiac muscle myosins were observed under rigor conditions (-Ca2+/+Ca2+). In the present work these studies have been extended to new more order-producing conditions (presence of ATP in the absence of Ca2+) aimed at arresting the relaxed structure in synthetic filaments of both fast and slow skeletal muscle myosin. Filaments were formed from column-purified myosins (rabbit fast skeletal muscle and rabbit slow skeletal semimebranosusproprius muscle). In the presence of 0.1 mM free Ca2+, 3 mM Mg2+ and 2 mM ATP (activating conditions) these filaments had a spread structure with a random arrangement of myosin heads and subfragments 2 protruding from the filament backbone. Such a structure is indistinguishable from the filament structures observed previously for fast skeletal, cardiac (see reference cited above) and smooth (Podlubnaya et al., 1999, J. Muscle Res. Cell Motil. 20, 547-554) muscle myosins in the presence of 0.1 mM free Ca2+. In the absence of Ca2+ and in the presence of ATP (relaxing conditions) the filaments of both studied myosins revealed a compact ordered structure. The fast skeletal muscle myosin filaments exhibited an axial periodicity of about 14.5 nm and which was much more pronounced than under rigor conditions in the absence of Ca2+ (see the first reference cited). The slow skeletal muscle myosin filaments differ slightly in their appearance from those of fast muscle as they exhibit mainly an axial repeat of about 43 nm while the 14.5 nm repeat is visible only in some regions. This may be a result of a slightly different structural properties of slow skeletal muscle myosin. We conclude that, like other filaments of vertebrate myosins, slow skeletal muscle myosin filaments also undergo the Ca2+-induced structural order-disorder transitions. It is very likely that all vertebrate muscle myosins possess such a property.

[Role of myosin light chains in regulating muscle contraction]. / Rol' legkikh tsepei miozina v reguliatsii myshechnogo sokrashcheniia.

Current review is focused on regulatory functions of myosin light chains from different muscle types. Special attention is paid to myosin light chains from striated muscles. The present review considers mainly the relevant data provided after 1986.

[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]. / Otsutstvie sezonnykh adaptatsionnykh izmenenii v izoformnom sostave i funktsional'nykh svoistvakh belkov aktinsoderzhashchikh nitei skeletnyih myshts zimospiashhikh suslikov.

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.

[Changes in the isoform composition of the cytoskeletal protein titn--adaptation process in hibernation]. / Izmeneniia izoformnogo sostava tsitoskeletnogo belka taitina--adaptatsionnyi protsess pri gibernatsii.

Changes in the isoform composition of the elastic protein titin from skeletal and cardiac muscles of hibernating ground squirrels were revealed for the first time. It was shown that, upon hibernation, the molecular mass of titin decreases and its functional properties change as compared with the active state of the animal. The physiological significance of the changes in titin isoform composition for the inhibition of muscle contractile activity upon hibernation is discussed in connection with similar changes during some cardiomyopathies.

[Role of atrial myosin light chains in modulating the functional properties of myocardium]. / Rol' predserdnykh legkikh tsepei miozina v moduliatsii funktsional'nykh svoistv miokarda.

To elucidate the functional importance of the appearance of atrial myosin light chains (ALC) in ventricles in some cardiomyopathies, a partial (75%) substitution of myosin light chains 1 and 2 of the left ventricle for ALC-1 and ALC-2 was carried out in vitro. It is shown that this substitution does not lead to changes in shapes and sizes of the filaments formed by hybrid myosin but causes changes in the shape of myosin heads. The replacement of the light chains increases the actin-activated ATPase activity of hybrid myosin by 63%. The results obtained are evidence that the substitution of ventricle myosin light chains with atrial ones is of physiological importance for the improvement of myosin functional properties and thereby for the compensation of the insufficiency of myocardium in dilated cardiomyopathy. These data and the data on dynamics of ALC-1 in diseased ventricles are important for creating the prognostic test of dilated cardiomyopathy development based on the registration of changes in the isoform composition of cardiac myosin light chains.

[The behavior of titin and the proteins of its family from skeletal muscles of ground squirrel (Citellus undulatus) during hibernation and rats under conditions of simulated microgravity]. / Povedenie taitina i belkov ego semeistva v skeletnykh myshtsakh suslikov (Citellus undulatus) pri zimnei spiachke i krys v usloviiakh modeliruemoi mikrogravitatsii.

By the use of SDS PAGE, the behavior of titin and MyBP-C in fast (m. psoas) as well as titin and MyBP-X in slow (m. soleus) muscles of ground squirrels (Citellus undulatus) during hibernation was compared with the behavior of titin and MyBP-X in rat m. soleus under conditions of simulated microgravity. A decrease in the amount of titin 1 and MyBP-C relative to that of myosin heavy chains by approximately 30% and approximately 40%, correspondingly, in muscles of hibernating and arousing ground squirrels was revealed in comparison with active animals. No differences in the relative amount of MyBP-X in m. soleus of hibernating, arousing and active ground squirrels were found. Under conditions of simulated microgravity, a decrease in the amount of titin 1 by approximately 2 times and MyBP-X by approximately1.5 times relative to that of myosin heavy chains in rat m. soleus was observed. By the method of SDS PAGE modified by us, an almost twofold decrease in the amount of short isovariants of the titin N2A isoform relative to that of myosin heavy chains was shown in muscles of hibernating and arousing ground squirrels, whereas no changes were found in the amount of long titin isovariants. The conditions of simulated microgravity resulted in a twofold decrease in the relative amount of both short and long titin isovariants in rat m. soleus. The results indicate that hibernating ground squirrels have an evolutionarily determined adaptive mechanism of selective degradation of fast muscle fibers and preservation or increase of slow fibers, as the most economic and energetically advantageous, with proteins typical of them. The microgravitation of nonhibernating animals (rats) leads to a non-selective degradation of MyBP-X and titin isovariants, which contributes to considerable atrophy of soleus fibers.

[Correlation between Ca2+-dependent movement of crosslinks in myosin filaments and Ca2+-sensitive actin-activated ATPase of skeletal muscle myosin]. / Korreliatsiia mezhdu Ca2+-zavisimym dvizheniem mostikov v miozinovykh nitiakh i Ca2+-chuvstvitel'nost'iu aktin-aktiviruemoi ATFazy miozina skeletnykh myshts.

The dependence of actin-activated ATPase activity and myosin filament structure have been studied on Ca(2+)-concentration in the range between pCa 7.5 and pCa 4.6. Rabbit skeletal muscle myosin with dephosphorylated regulatory light chains column-purified with DEAE-Sephadex A-50 for the removal of minor proteins and actin without regulatory proteins have been used. Considerable increase in actomyosin ATPase activity (by 70%) is revealed with increasing Ca(2+)-level from pCa 7.5 up to pCa 4.6. Electron microscopic observations on the structures of reconstituted myosin filaments have revealed Ca(2+)-dependent movement of myosin cross-bridges (head + subfragment-2) from and to the backbone of myosin filaments. The correlation between the manifestation of Ca(2+)-sensitivity of ATPase properties of myosins and Ca(2+)-dependent mobility of cross-bridges has been established. In particular, the increase in the mobility of cross-bridges and their moving away from the surface of myosin filaments at pCa 4.6 correlates with the increase in actin-activated ATPase of the same myosin preparations. It is supposed that the interrelation between the above properties observed in in vitro system can be of importance for force generation and its regulation in muscle.

[The role of different neuromediator systems in regulating the reproduction of memory engrams in rats]. / Rol' razlichnykh neiromediatornykh sistem v reguliatsii vosproizvedeniia éngramm pamiati u krys.

In experiments on 796 white rats the role was studied of various neurotransmitter systems (choline-, adreno-, serotonin-, dopamine-, and GABA-ergic) in regulation of processes of engrams reproduction, determined by tests of conditioned passive- and active-defensive reactions in comparison with changes of spontaneous motor activity and oriented reaction. Correlations are analyzed between the changes of animals behavioural reactions in conditions of pharmacological control of activity of the studied neurotransmitter systems.