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 space flight on bone formation and resorption.

Samples of femurs and tibiae of male Wistar rats subjected to a 13 day space-flight on the biosatellite Cosmos 1887--were investigated and compared with vivarium and synchronous controls or immobilized rats, using histological and histomorphometric methods. 1. After flight in the metaphysis of bones the density and volume of the spongious trabeculae diminished significantly indicated by the Sv and Vv histomorphometric values and histological data comparing to the controls. In the diaphysis, the density of trabeculae decreased too. 2. In the flight group significant suppression of bone formation was determined by histological and histomorphometric (decrease of the OS, OB and OBI values) methods. 3. In the flight group according to the histological pictures the signs of bone resorption (increase of Hoswship's lacunae, osteoclastic activity, structural rarefication of spongious and cortical bones, osteon disintegration, osteocytic osteolysis) were revealed, which was substantiated by the histomorphometric results (increase of osteoclastic index: OCI). 4. Significant differences between flight and immobilized groups were not determined, except the osteoid value, which was increased in the case of immobilization. 5. Some histomorphometric values related to bone formation of synchronous control group showed close relationship rather to the flight group than to the vivarium control group.

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.

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.

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 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.

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.

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.

A new apex-ejecting perfused rat heart preparation: relation between coronary flow and loading conditions.

The isolated perfused rat heart is an important experimental preparation for both mechanical and biochemical studies. In order to define better the relationship between coronary flow and loading conditions, a new preparation was developed in which the left ventricle ejected through the apex, while the aortic perfusion pressure could be separately controlled at a higher level than the apex afterload. Results were compared with a standard aortic perfused and ejecting preparation. All analyses were made at low calcium concentration (1.6 mmol X litre-1) for reducing cardiac performance. Coronary flow was related to perfusion pressure in the aortic ejecting preparation when the aortic afterload chamber was between 6.0 and 9.3 kPa (45 and 70 mmHg). Coronary autoregulation was demonstrable in the apex ejecting preparation irrespective of the height of the apex afterload chamber and the aortic ejecting preparation when the aortic chamber was between 11.0 and 16.0 kPa (83 and 120 mmHg). Following the addition of 10(-6) mol X litre-1 adenosine, there was significant coronary vasodilatation, and flow became pressure dependent in all cases. In the apex-ejecting preparation, with a high aortic pressure, coronary flow remained at relatively fixed level, and increases in oxygen demand were met by increasing oxygen extraction. Thus, in this preparation oxygen extraction was directly related to workload. With abrupt increases in afterload, going from 6.0 to 9.3 kPa (45 to 70 mmHg) to a higher level, there was evidence of transient hypoxia with the aortic ejecting but not the apex ejecting preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Effect of weightlessness on the function of rat skeletal muscles on the biosatellite "Cosmos-1129".

Isometric tension of glycerinated fibrils of different skeletal muscles was studied in white rats carried in the biosatellite "Cosmos-1129" for 18.5 days. Expression and trends of the changes in contractile properties of muscle preparations depend on their functional specialization. The most sensitive reaction was displayed by the soleus muscle which consists predominantly of slow fibres.