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Biomedical subjects

T L Nemirovskaya

Publications and source records attributed to T L Nemirovskaya.

At least 19 recordsLinked to original sources
PubMed2004

Effects of deafferentation on the size and myosin phenotype of muscle fibers on stretching of the rat soleus muscle in conditions of gravitational unloading.

The aim of the present work was to assess the contributions of the reflex and local components to preventing decreases in the size and changes in the ratio of fibers containing the slow and fast isoforms of myosin heavy chains during chronic stretching of a postural muscle in rats in conditions of gravitational unloading. A unilateral surgical deafferentation method was used. The results demonstrated that deafferentation of the hindlimb had no effect on preventing reductions in muscle fiber size in conditions of chronic muscle stretching in conditions of gravitational unloading. The results obtained from these experiments did not support the hypothesis that the predominant contribution to preventing the development of atrophic changes comes from activation of muscle afferents in chronic stretching of the unloaded muscle. Deafferentation of both suspended animals and those with normal motor activity led to increases in the proportion of soleus muscle fibers containing the slow isoforms of myosin heavy chain.

Animals↗
PubMed2004

Afferent and peripheral control of muscle fiber properties during gravitational unloading.

The present paper covers two series of the experiment studies performed in attempt to analyze the support-triggered cellular mechanisms, controlling the maintenance of tonic muscle fiber characteristics. Exposure to 7 day dry immersion induced significant decline of the human soleus single fiber peak isometric tension and the Ca(2+)-sensitivity of myofibrils. 30-40% losses of the relative content of titin and nebulin were found after immersion. The application of the plantar support stimulation device prevented all these alterations. In the second experimental series the treatment of hindlimb suspended rats with the Ca(2+)-binding agent (EGTA) allowed to prevent or attenuate all the above mentioned unloading-induced soleus fiber alterations. Thus it is concluded that resting Ca2+ accumulation in the unloaded fibers may be among the mechanisms involved in the changes of fiber properties during unloading.

Animals↗
PubMed2003

Characteristic of changes in the structure and metabolism of the vastus lateralis muscles in monkeys after space flight.

Monkeys subjected to space flight were found to have significant decreases in the sizes of slow and rapid fibers in the vastus lateralis muscle, due not only to weightlessness but also, to some extent, to restriction of movement activity within the capsule. The quantity of total protein in muscle fibers did not decrease. The respiratory peak in the pool of vastus lateralis muscle fibers decreased after space flight, as did the activity of oxidative enzymes (particularly in rapid fibers of the vastus lateralis muscle).

Animals↗
PubMed2003

Effects of weightlessness and movement restriction on the structure and metabolism of the soleus muscle in monkeys after space flight.

After humans and animals have been in conditions of real and modeled weightlessness, the most marked changes are seen in the "slow" tonic muscles, particularly soleus. Studies of the effects of weightlessness and movement restriction on the soleus muscle in monkeys demonstrated significant reductions in the sizes of slow and rapid fibers due mainly to the actions of real weightlessness (rather than movement restriction in the space capsule). Protein loss in soleus muscle fibers in monkeys following space flight was more marked than loss of other components, including water. The level of atrophy of soleus muscle fibers in these conditions was greater than the decrease in the number of capillaries. Succinate dehydrogenase activity in soleus muscle fibers decreased proportionally to the reduction in fiber size.

Animals↗
PubMed2002

Role of afferent control in maintaining structural and metabolic characteristics of stretched soleus in rats exposed to hindlimb suspension.

It is known that gravitational unloading (GU) induces atrophy of skeletal muscles and slow-to-fast muscle fiber (MF) transformation. Stretching of m. soleus prevents those changes, probably afferent information from the stretched muscle acting as triggering mechanism. It was shown that EMG of suspended animals or of stretched muscle is similar to that of control animals. Our study was aimed at revealing contribution of the afferent information from stretched m.soleus exposed to GU in maintenance of cross-sectional area (CSA) of MF and of myosine heavy chains and oxidative potential of skeletal muscles.

Journal Article↗
PubMed2002

Structural and metabolic characteristics of human soleus fibers after long duration spaceflight.

The fiber size decline, alterations in fiber metabolic potential and increase of connective tissue component were shown in human m. vastus lateralis after short and long-duration space flights and in m.soleus and m.vastus lateralis after 120 day head down tilt bed rest. It is known from rat and monkey studies that the exposure to weightlessness leads to the most pronounced changes in postural muscles, e.g. m.soleus. It was shown that 17 day space flight induced significant decrease of fiber cross-sectional area and slow-to-fast fiber type transformation in human soleus. But in the cited work the fiber population under study was limited like in most single fiber technique analyses. The present study was purposed to investigate the structural and metabolic properties of soleus muscle in Russian cosmonauts exposed to 129-day space flight on board of the International Space Station.

Journal Article↗
PubMed2002

Effects of Ca2+(-)binding agent on unloaded rat soleus: muscle morphology and sarcomeric titin content.

It had been hypothesized and recently shown that the exposure to gravitational unloading brought out to sufficient accumulation of Ca2+ in the myoplasm of soleus muscle fibers. Some authors believe that this dramatic Ca2+ accumulation induces the muscle protein degradation (including cytoskeletal proteins) by means of Ca 2(+)-activated proteases. For instance, the loss of giant sarcomeric cytoskeletal protein titin which is believed to determine the elasticity properties of muscle fibers, may contribute to the fiber stiffness decrease under unloading conditions. The study was designed to test the hypothesis suggesting that intracellular Ca2+ binding by means of EDTA administration would allow to attenuate hypogravity-induced atrophic changes including changes in myofibrillar proteins of skeletal muscle fibers.

Journal Article↗
PubMed2002

Mitochondrial adaptations in skeletal muscle cells in mammals exposed to gravitational unloading.

It is known that exposure to actual or simulated weightlessness is often accompanied by decreased muscle dynamic performance, and increased level of blood lactate accumulation. Decreased mitochondrial content found in fibers of the working muscles is considered to be one of the possible causes for those changes. Studies on oxidative potential of the muscle cell (i.e. capacity of the cell to oxidative energy production) under conditions of altered gravity have been carried out since late 70-ties. It was shown that the relatively short term spaceflight and hindlimb suspension induced significant decrease oxidative enzyme activities and mitochondrial volume density in rat fast muscle. However postural soleus muscle failed to exhibit similar changes, although the absolute mitochondrial content was found to be sufficiently lower after exposure to simulated microgravity. This phenomenon allowed to conclude that the pronounced soleus fiber atrophy masked the proportional absolute decrease in oxidative potential which failed to be revealed as subsequent changes in mitochondrial volume density and oxidative enzyme activity. It is also important, that biosatellite studies exposed considerable changes in mitochondria distribution pattern inside m. soleus fibers: volume density of mitochondria (and, correspondingly, activity of oxidative enzymes) increases (or does not change) in the center of fiber, and decreases at its periphery, in subsarcolemmal area. However the time course of mitochondrial alterations development (particularly during long-duration exposures to real or simulated microgravity) and some peculiarities of the mitochondria distribution were not described yet. Also, materials dealing with simultaneous time-course comparative analysis of mitochondrial characteristics and indices of physiological cost of submaximal exercise are very rare. The present paper is purposed to compare the data, obtained in several experimental studies, allowed to analyze the possible contribution of muscle mitochondria changes to changes in metabolic cost of submaximal exercise and the time-course dynamics of mitochondrial characteristics under conditions of actual or simulated gravitational unloading.

Journal Article↗
PubMed2001

Dystrophin in limb skeletal muscle fibers and creatinkinase leakage after acute +3 Gz acceleration in rhesus monkeys.

Intensive muscle tension induces significant blood accumulation of enzymes and structural proteins of the muscle origin. Altered macromolecular permeability of the sarcolemma is attributed to integrity of sarcolemmal cytoskeleton, mainly to dystrophin-sarcoglycan (DSG) complex. It is known that intensive tension of the antigravity extensor muscles is observed under conditions of gravitational overloading. We assumed that acute exposure to hypergravity would lead to serum accumulation of creatine phosphokinase (CK) associated with considerably altered integrity of the dystrophin layer in fibers of extensor muscles.

Acceleration↗
PubMed2000

Effects of beta(2)-agonist clenbuterol on biochemical and contractile properties of unloaded soleus fibers of rat.

The effects of clenbuterol beta(2)-agonist administration were investigated in normal and atrophied [15-day hindlimb-unloaded (HU)] rat soleus muscles. We showed that clenbuterol had a specific effect on muscle tissue, since it reduces soleus atrophy induced by HU. The study of Ca(2+) activation properties of single skinned fibers revealed that clenbuterol partly prevented the decrease in maximal tension after HU, with a preferential effect on fast-twitch fibers. Clenbuterol improved the Ca(2+) sensitivity in slow- and fast-twitch fibers by shifting the tension-pCa relationship toward lower Ca(2+) concentrations, but this effect was more marked after HU than in normal conditions. Whole muscle electrophoresis indicated slow-to-fast transitions of the myosin heavy chain isoforms for unloaded and for clenbuterol-treated soleus. The coupling of the two latter conditions did not, however, increase these phenotypical transformations. Our findings indicated that clenbuterol had an anabolic action and a beta(2)-adrenergic effect on muscle fibers and appeared to counteract some effects of unloading disuse conditions.

Adrenergic beta-Agonists↗
PubMed2000

Ultrastructure of skeletal muscles of rhesus monkeys after spaceflight.

The ultrastructure of myofibrillar and mitochondrial apparatus of m. soleus and m. vastus lateralis of Bion 11 monkeys was investigated. In both muscles, the volume density and the mean area of myofibrils increased insignificantly and their number decreased; in m. soleus the mean area of mitochondria increased significantly and in m. vastus lateralis insignificantly.

Adaptation, Physiological↗
PubMed2000

Influence of repetitive Gz acceleration on structural and metabolic profile of m. vastus lateralis in monkeys exposed to 30 day bedrest.

It was shown that changes in structural and metabolic indices of extensor muscles of the lower extremities were usually found in man after exposure to space flight or to bed rest. Similar changes were also observed in monkeys, space-flown on "Kosmos" biosatellites. Response to weightlessness and to restraint was found to be different in m. soleus and in m. vastus lateralis. Therefore, it is important to study structural and metabolic changes of m. vastus lateralis fibers under conditions of gravitational unloading in monkeys, who have motor apparatus similar to that of man, and are much more fruitful object of research. It is assumed that artificial gravity can serve as a countermeasure, aimed at diminishing effects of gravitational unloading. We have studied the effect of repeated gravity overloading, created by means of a centrifuge, on structural and metabolic indices of monkey m. vastus lateralis at the background of 30 day head down tilt bed rest (BR).

Acceleration↗
PubMed2000

Muscle derived serum enzyme accumulation after +Gz acceleration test in Rhesus monkeys exposed to bed rest.

It is known that several hours of intensive muscle tension result in accumulation of muscle derived enzymes and structural proteins (see review by Clarkson, 1997). We have assumed that, firstly, acute exposure to hypergravity may induce accumulation of serum creatine phosphokinase (CPK), and, secondly, level of that accumulation may be considerably altered after long term hypokinesia.

Animals↗
PubMed1999

Influence of single hindlimb support on fiber characteristics of unloaded skeletal muscle.

The unweighting and/or immobilization in the shortened position leads to muscle atrophy, slow-to-fast transformation and biochemical alterations in muscle fibers. This process could be prevented by the stretching or loaded contraction. On the other hand Kozlovskaya et al. demonstrated triggering of postural synergies due to using artificial support simulator in spaceflight. The study was aimed to test if the plantar support stimulation might prevent muscle atrophy, slow-to-fast transformation of muscle fibers and oxidative potential alteration during gravitational unloading.

Animals↗
PubMed1998

What is the trigger mechanism for changes of the oxidative potential in skeletal muscle?

It is known that the long-duration decline of high-energy phosphates(HP) level in skeletal muscles, induced by administration of beta-guanidinpropionic acid (beta-GPA), is followed by the increase of mitochondrial enzyme activities (MEA). The same increase of MEA was observed in the course of physical exercise training. The decrease of MEA and at the same time the increase of HP levels were found under gravitational unloading. If changes in HP level are believed to trigger on the alterations in MEA, the increase of HP levels in muscles should lead to decline of MEA as well. The present work was purposed to reveal if the changes in HP level under different contractile activity levels are associated with the changes of oxidative potential in the skeletal muscles.

Animals↗
PubMed1997

Muscle atrophy and hormonal regulation in women in 120 day bed rest.

It is known, that exposures to real and simulated weightlessness results in pronounced reduction of the cross-sectional area (CSA) of slow-twitch(ST) and fast-twitch(FT) fibers of mammalian muscle. After space flights of various durations, head-down tilt bedrest, and 7-days of dry immersion sufficient [correction of isufficient] reductions of CSA of both fiber types were observed in man and in the majority of these cases the atrophy levels of ST and FT fibers were similar. It is well-known, that elevated contractile activities of muscle system attenuate muscle atrophy development. It remains still unclear which fiber type is more susceptible to training effects. Among physiological mechanisms involved in the process of microgravity-induced atrophy development which are supposed to be the most important are the profound decrease of a mechanical tension of muscle fibers in situ and alterations in hormonal control of muscle protein metabolism. But it is not known yet if the hormonal changes in the course of exposure to gravitational unloading match somehow the time-course of muscle fiber size reduction. The aim of the study was to investigate the time-course of muscle fiber atrophy development and changes in plasma hormone levels in the course of long-duration BR with and without high-intensity locomotor interval physical training.

Adenosine Triphosphatases↗