Effect of short- and long-term spaceflight on the contractile properties of rat skeletal muscles with different functions.

In the Cosmos biosputnik 1514, 1667, 1887, 2044 and 1129 the rats 5, 7, 12,5, 15, 18,5 days were in weightlessness state. Due to the adaptation of the skeletal muscles' weightlessness the adaptation was different in various muscles, which depends on the time of participation in antigravitation, the composition of the fibers and from the biometrical characteristics. In different muscles, the changing of the metabolism and the structure of the muscles more than likely in connection with the changing of the myosin subordinate unit compositions. In our experiments we had studied, as to how the muscular atrophy changes, does it increase all the time, or does it balances out after reaching a certain stage.

Effect of short-term spaceflight on the contractile properties of rat skeletal muscles with different functions.

In the biosatellites "Cosmos-1514" and "Cosmos-1667" rats were exposed to weightlessness in the space for either 5 or 7 days. The contractile properties of the soleus, extensor digitorum longus (EDL), brachialis, plantar, gastrocnemius and triceps (caput mediale) muscles were studied after return to earth. The muscles of animals living freely (vivarium group) and animals kept under conditions identical to those on the biosatellite (synchronous group) served as controls. The myofibrils were preserved by glycerol treatment. The ATP-Ca+(+)-induced isometric tension as well as the speed of contraction were registered, through a signal transformer, on a potentiometric recorder. The experimental results are concomitantly recorded numerically and graphically on a Citizen 1200 printer and analyzed with a Commodore 128D computer. During the short-term spaceflight the greatest weight loss and decrease of contractile power was seen in the slow soleus muscle, i.e. weightlessness and immobilization led to the degeneration and weakening of mainly the tonic muscle fibres. Nevertheless after the short-term spaceflight, even with the present improved and sophisticated methods, the authors were unable to demonstrate, changes indicating muscle transformation which had been previously seen in rats exposed to weightlessness for 18.5 days.

Effects of skeletal muscle myosin light chain phosphorylation on synthetic actomyosin ATPase activity and superprecipitation.

In the present study the effect of phosphorylation of skeletal muscle myosin light chains on the interaction between myosin and actin has been investigated. The actomyosin ATPase activities were determined for synthetic actomyosins formed from either phosphorylated or non-phosphorylated myosin and pure actin, with the help of the luciferin-luciferase system. The contractile properties of our preparations were simultaneously studied by the superprecipitation model. Phosphorylated form of myosin had lower actin-activated ATPase activity at particular conditions studied. In agreement with this, superprecipitation of phosphorylated actomyosin was delayed. On the basis of these results one can expect that phosphorylation of myosin light chains modulates contractile properties of intact skeletal muscle.

Quantitative alterations of intramuscular connective tissue in calf muscles of the rat during combined hypoxia and hypokinesia.

The investigations were designed to study the long-term effect of hypoxia, hypokinesia and of combined hypokinesia and hypoxia on the skeletal muscle in the rat. In the muscles of the hypoxic and hypokinetic animals serious degenerative changes were found and the fibre-type ratio was altered. In the hypoxic animals moderate fibrosis was revealed. In the hypokinetic, and hypokinetic + hypoxic animals the amount of connective tissue was 5 to 10-fold greater in the calf muscles as compared to the control.

Contractile properties of chick embryo muscles in development.

In this paper we report on the observation of two parameters of embryonic muscles which show the functional activity of myofibrillar ATPase activity of embryonic muscles and superprecipitation (SP) of natural actomyosin. Our results indicate that, during the embryonic period, the myofibrillar ATPase activity and the SP of actomyosin significantly increased, the rate of this increase being different for leg and breast muscles.

The effect of ipriflavone treatment on osteoporosis induced by immobilization.

The purpose of these experiments was to study the effect of Ipriflavone (7 isopropoxy-isoflavone) on the osteoporosis induced by immobilization. The immobilization was produced by plaster cast of the right hind limb in young and old rats. Ipriflavone was administered via a gastric tube in a daily dose of 40 mg/kg body weight for 8 weeks. On the basis of histological and histomorphometric examinations of the tibia, results of Ipriflavone treatment are the following: 1) The decrease in the density and volume of spongy trabecules was less apparent in both meta- and diaphysis; 2) The amount of persisting cartilage core and structural rarefication of trabecules were diminished; 3) In the metaphysis osteoblastic activity was considerably enhanced; 4) Bone resorption and cortical thinning were decreased; 5) Bone remodeling was increased subperiosteally and to small extent also endosteally; 6) The treatment did not prevent the development of osteoporosis but significantly diminished it.

[ATPase activity and the contractile capacity of the muscle tissue in chick embryos during development]. / ATFaznaia aktivnost' i "sokratitel'naia sposobnost'" myshechnoi tkani kurinykh émbrionov v protsesse razvitiia.

The value of ATPase activity of the myofibril preparations and the value and duration of actomyosin superprecipitation were estimated for different muscles during the chick embryonic development. The ATPase level increases during embryogenesis 4.5-fold, in the leg muscle this change takes place distinctly earlier than in the leg muscle. The value and rate of actomyosin superprecipitation also markedly increase, to a lesser extent for m. soleus than for m. pectoralis. It is suggested that these changes and differences are mainly due to the delay in synthesis of certain types of the embryonic myosin light chains.

Radiological investigation of alterations in the rat femur after long-term immobilization.

The right hind limb of female rats was immobilized by plaster cast. Following 8 weeks of immobilization the alterations were compared with either the contralateral extremity of the same rat or with the extremities of non-immobilized animals. The femurs were investigated by microradioscopic, morphometric, densitometric and atom absorption methods. The results obtained have unequivocally shown that long-term immobilization by plaster cast leads to development of osteoporosis in the rat. Even though no considerable loss of calcium could be demonstrated when calculated in terms of unit layer thickness quantitative analysis of the bone revealed a high degree of osteopenia.

Effect of plaster-cast immobilization on the bone.

Plaster-cast of the right hind limb resulted in immobilization osteoporosis in rats. The alteration was characterized by loss of the bony substance as well as by a partial transformation of lamellar bone to primordial osseous tissue. In the basis of histological and histomorphometric findings, an accelerated osteoclastic activity, an increased osteocytic osteolysis and a decreased ossification are responsible for the observed changes.

Contraction induced by antibodies to paramyosin in glycerinated fibers of Barnacle giant muscle in an ATP-deficient medium: a possible function of paramyosin.

Glycerinated giant muscle fibers of the barnacle Balanus rostratus in an ATP-deficient solution respond to antibodies to paramyosin (aPM) by an isometric tension development followed by an immediate spontaneous relaxation. The aPM presence does not affect the subsequent contraction and relaxation of the fibers in suitable ATP-containing media. The effects of ATP and aPM present together in a contracting medium are additive. The aPM effect is caused assumedly by a sudden shortening of some highly elastic connecting filaments which are linked in a stretched and strained state to the thick filament by its paramyosin, aPM dissociates this link. Possible specific functions of paramyosin in various types of muscles are discussed.

The role of DTNB light chain in the contractile properties of skeletal muscle.

The mechanical and molecular dynamical properties of the glycerinated muscle fibres from m. psoas of rabbit were investigated after treatment with 5,5'-dithiobis/2-nitrobenzoate (DTNB). After DTNB treatment the fibre bundles shortened and exerted force in ATP-relaxing solution. The rate of the ATP hydrolysis in relaxation-inducing medium increased significantly after DTNB treatment, and simultaneously the amount of the LC2(DTNB) light chain decreased to 40 per cent of the original value measured by gel electrophoresis. The electron paramagnetic resonance spectra of muscle fibres labelled with maleimide spin label after DTNB treatment exhibited high degree of order of label in rigor, but this order decreased after shortening. The experiments support the assumption that, in vertebrate skeletal muscles, besides the troponin-tropomyosin regulation system which developed later in evolution, the LC2 light chain should maintain some regulatory properties.

[The paramyosin function in glycerinated muscle fibers during blocking with antibodies of its contacts with structural proteins]. / Izuchenie funktsii paramiozina v glitserinizirovannykh voloknankh myshts pri blokirovanii antitelami ego kontaktov so strukturnymi belkami.

Antibodies to paramyosin (APM) induce a partial decrease of the isometric tension in glycerinated fibres of the Anodonta cygnea catch muscle in the presence of ATP and Ca2+; the myofibrillar Mg2+ ATPase increases concomitantly. Assumedly paramyosin inhibits the cross-bridges unlocking, retaining them mechanically in a locked state. The fibres of barnacle giant muscle in an ATP deficient solution respond to APM by transient isometric tension development. A model for the participation of paramyosin in the contractile process is proposed. In both muscle types paramyosin hinders the functioning of certain elements of the contractile machinery.

Effect of DTNB-treatment on Ca++-sensitivity of superprecipitation and ATPase activity of actomyosin.

A light chain of 18 000 daltons of native actomyosin isolated from rabbit skeletal muscle was removed by DTNB-treatment. Investigated were the differences in superprecipitation and ATPase activity of LC2-deficient and control actomyosin. The superprecipitation of control actomyosin develops in two phases, with high amplitude and kinetics dependent on the Ca++ concentration. On the other hand, superprecipitation of treated actomyosin develops in a single phase, with low amplitude and a kinetics independent of the Ca++ concentration. The partial lack of LC2 leads to the loss of Ca++-sensitivity of ATPase activity. On the basis of the results, LC2 has been assumed to fix that conformation state of myosin heads which is required for the functioning of the troponin system on the one hand, and a cooperation between myosin heads on the other. The regulatory function of LC2 is manifest in controlling the actin-myosin-ATP interaction, at the activated state of the troponin system, in an extent depending on the actual Ca++ concentration.

Histochemical and biochemical alterations in skeletal muscles of rats during combined chronic hypoxia and hypokinesia.

This investigation was designed to study the long term effect of combined hypokinesia and hypoxia on the skeletal muscle. In the muscles of the hypoxic and hypokinetic animals, serious degenerative changes were found and the fibre type ratio was alterated. The malate dehydrogenase activity was decreased, and both LDH and MDH isoenzymes pattern were alterated.

The effect of adenosine diphosphate on the interaction of actin-myosin-adenosine triphosphate.

It was shown in experiments made on natural actomyosin of rabbit skeletal muscle that ADP possesses direct and indirect effects on superprecipitation. The presence of ADP increases the turbidity of the actomyosin suspension. An optimal ATP/ADP ratio may help the development and existence of a PC conformer of actomyosin corresponding to a myosin-ADP-actin-myosin-ATP complex. In this complex the extent of actin-activation is controlled by the cooperativity between the two myosin heads which, on the other side, may regulate in vivo the optimal transformation of the chemical energy of ATP for mechanical work.

Effect of immobilization on some glycolytic enzymes of skeletal muscle.

The effect of immobilization by plaster cast was studied on the activities of phosphoglucomutase (PGM), pyruvate kinase ( PyK ) and cAMP-dependent protein kinase in fast (extensor digitorum longus [EDL]), and slow (soleus) muscles of rats. In control untreated animals, PGM and PyK activities are 3 and 5 fold higher respectively in EDL than in soleus in correlation with the high glycolytic activity of fast muscles. During the four weeks period of immobilization a 20% decrease occurred in PGM activity, to which no limiting role in glycolysis is attributed, while PyK which has a regulatory function, showed a 35% decrease in EDL; at the same time in the soleus the activity of these enzymes did not change. The decrease of PGM and PyK activity in EDL diminished the difference between the slow and fast muscles, and it was evaluated as a tendency to dedifferentiation (transformation). The activity of cAMP-dependent protein kinase, in contrast to the glycolytic enzymes, was higher in the soleus than in the EDL and during immobilization it did not change significantly in either the muscles.

Step-like superprecipitation of actomyosin.

The superprecipitation of natural actomyosin prepared from rabbit skeletal muscle shows a step-like character under physiological conditions (KCl 0.14 M, ATP 0.001 M). Alkali metal cations applied in the same (0.14 M) concentration cause a delay according to the Hofmeister sequence, while in their presence the step-like character of superprecipitation is retained. Reduction of the Ca2+ concentration also causes a delay in the development of superprecipitation, but its step-like character is retained in this case, too. Increasing the Mg2+ concentration in the medium causes a delay or disappearance of superprecipitation and modifies it to occur in a single step. It is assumed that the actions studied exert, their effect in a combined way actin directly or indirectly on the interaction of actin and myosin.

Effect of immobilization on the enzymes of glycogen metabolism.

Activity of the enzymes regulating glycogen metabolism was determined for glycogen phosphorylase (Ph), phosphorylase kinase (PhK) and glycogen synthetase (GS) in fast extensor digitorum longus (EDL) and slow (soleus) muscles of rats following immobilization by plastering. It was shown that the activity not only of Ph but also of PhK was about 8 times higher in the EDL than in the soleus muscle in correlation with the higher glycogenolytic activity of fast muscles. The activity of GS was approximately similar in the two muscles. PhK activity decreased significantly in the immobilized EDL muscle while in the soleus an early reduction of GS activity ensued. Reduction of the activity of the glycogenolytic enzymes caused dedifferentiation in the muscles with anaerobic metabolism and containing large amounts of glycogenolytic enzymes. The similar rate of Ph and PhK in fast and slow muscles, as well as the similar rate of their reduced activity, during immobilization indicated a close correlation between the two enzymes and raised the possibility of a combined regulation of their turnover.

Effect of antibodies to light meromyosin on glycerinated muscle fibres and on actomyosin adenosinetriphosphatases.

The conformation change of light meromyosin influences the myosin and actin interaction, the myosin ATPase activity [22]. Starting from these data the specificity of the phenomenon has been investigated. The effect of LMM1, LMM- and LMM1-antibodies was studied on the isometric tension and relaxation of glycerol extracted muscle fibres. LMM1 was found to relax the fibres isometrically contracted by ATP-Ca2+; anti-LMM and anti-LMM1 markedly accelerated the development of isometric tension and inhibited the relaxation of ATP contracted glycerinated muscle fibres; in the presence of anti-LMM the ATPase rate of glycerinated myofibrils was slightly augmented. These results seem to indicate that LMM1 governs the actin binding site function of myosin and controls its affinity to actin. It is supposed that the reaction of myofibrils with specific LMM antibodies induced a transconformation in the myosin head increasing the affinity to actin of myosin.