Responses of neuromuscular systems under gravity or microgravity environment.

Hindlimb suspension of rats induces induces fiber atrophy and type shift of muscle fibers. In contrast, there is no change in the cell size or oxidative enzyme activity of spinal motoneurons innervating muscle fibers. Growth-related increases in the cell size of muscle fibers and their spinal motoneurons are inhibited by hindlimb suspension. Exposure to microgravity induces atrophy of fibers (especially slow-twitch fibers) and shift of fibers from slow- to fast-twitch type in skeletal muscles (especially slow, anti-gravity muscles). In addition, a decrease in the oxidative enzyme activity of spinal motoneurons innervating slow-twitch fibers and of sensory neurons in the dorsal root ganglion is observed following exposure to microgravity. It is concluded that neuromuscular activities are important for maintaining metabolism and function of neuromuscular systems at an early postnatal development and that gravity effects both efferent and afferent neural pathways.     

Interrelationships of contraction time, Vmax, and myosin ATPase after spinal transection

Interrelationships of selected mechanical and biochemical properties of hindlimb extensor muscles following low thoracic cord transection were studied. Kittens were spinalized (Sp) at 2 wk and maintained for 6-12 mo. Some Sp animals were exercised (Sp-E) on a treadmill 25-30 min/day, 5 days/wk. In situ contractile properties of the slow-twitch soleus (SOL) and fast-twitch medical gastrocnemius (MG) muscles of normal (N), Sp, and Sp-E cats were determined. Exercise did not affect most parameters; thus Sp and Sp-E groups are considered collectively. The cross-sectional areas (CSA) of the SOL and MG decreased by 43 and 32%, respectively. Specific tension (tension/CSA) was maintained in the SOL but decreased (P less than 0.05) in the MG. Contraction time (CT) and half-relaxation time were significantly shorter in the SOL but unchanged in the MG. Maximum shortening velocity (Vmax) and myosin ATPase (mumol X mg-1 X min-1) increased (P less than 0.05) in the SOL of both groups and the MG of Sp. Frequency-tension responses of both muscles shifted toward that resembling a "faster" muscle. These results substantiate the existence of relatively independent regulatory mechanisms for Vmax and CT and show that myosin ATPase levels are more closely related to Vmax than CT. Although the changes in the SOL were consistent with the hypothesis that slow fibers are converted to fast, the elevated Vmax and myosin ATPase of the MG suggest that significant changes also occur within a "fast" fiber-type category.     

Enzyme profiles of single muscle fibers never exposed to normal neuromuscular activity.

Do muscle fiber properties commonly associated with fiber types in adult animals and the population distribution of these properties require normal activation patterns to develop? To address this issue, the activity of an oxidative [succinic dehydrogenase (SDH)] and a glycolytic [alpha-glycerophosphate dehydrogenase (GPD)] marker enzyme, the characteristics of myosin adenosinetriphosphatase (myosin ATPase, alkaline preincubation), and the cross-sectional area of single fibers were studied. The soleus and medial gastrocnemius of normal adult cats were compared with cats that 6 mo earlier had been spinally transected at T12-T13 at 2 wk of age. In control cats, SDH activity was higher in dark than light ATPase fibers in the soleus and higher in light than dark ATPase fibers in the medial gastrocnemius. After transection, SDH activity was similar to control in both muscles. GPD activity appeared to be elevated in some fibers in each fiber type in both muscles after transection. The cross-sectional areas most affected by spinal transection were light ATPase fibers of the soleus and dark ATPase fibers of the medial gastrocnemius, the predominant fiber type in each muscle. These data demonstrate that although the muscle fibers of cats spinalized at 2 wk of age presumably were never exposed to normal levels of activation, the activity of an oxidative marker enzyme was maintained or elevated 6 mo after spinal transection. Furthermore, although the absolute enzyme activities in some fibers were elevated by transection, three functional protein systems commonly associated with fiber types, i.e., hydrolysis of ATP by myosin ATPase and glycolytic (GPD) and oxidative (SHD) metabolism, developed in a coordinated manner typical of normal adult muscles.     

ROS-mediated decline in maximum Ca2+-activated force in rat skeletal muscle fibers following in vitro and in vivo stimulation

We hypothesised that normal skeletal muscle stimulated intensely either in vitro or in situ would exhibit reactive oxygen species (ROS)-mediated contractile apparatus changes common to many pathophysiological conditions. Isolated soleus (SOL) and extensor digitorum longus (EDL) muscles of the rat were bubbled with 95% O(2) and stimulated in vitro at 31°C to give isometric tetani (50 Hz for 0.5 s every 2 s) until maximum force declined to ≤30%. Skinned superficial slow-twitch fibers from the SOL muscles displayed a large reduction (～41%) in maximum Ca(2+)-activated specific force (F(max)), with Ca(2+)-sensitivity unchanged. Fibers from EDL muscles were less affected. The decrease in F(max) in SOL fibers was evidently due to oxidation effects on cysteine residues because it was reversed if the reducing agent DTT was applied prior to activating the fiber. The GSH:GSSG ratio was ～3-fold lower in the cytoplasm of superficial fibers from stimulated muscle compared to control, confirming increased oxidant levels. The presence of Tempol and L-NAME during in vitro stimulation prevented reduction in F(max). Skinned fibers from SOL muscles stimulated in vivo at 37°C with intact blood supply also displayed reduction in F(max), though to a much smaller extent (～12%). Thus, fibers from muscles stimulated even with putatively adequate O(2) supply display a reversible oxidation-induced decrease in F(max) without change in Ca(2+)-sensitivity, consistent with action of peroxynitrite (or possibly superoxide) on cysteine residues of the contractile apparatus. Significantly, the changes closely resemble the contractile deficits observed in a range of pathophysiological conditions. These findings highlight how readily muscle experiences ROS-related deficits, and also point to potential difficulties when defining muscle performance and fatigue.     

A histochemical and electron microscopic study of a fast- and a slow-twitch muscle in genetically spastic mice

Fast and slow muscle fibers were studied in the flexor digitorum longus (FDL) and soleus (SOL) muscles, respectively, in control and spastic mice. HIstochemical and electron microscopic studies indicated an increased number of mitochondria, a decreased deposition of glycogen and a vesiculation and distension of the sarcoplasmic reticulum in many fast-twitch fibers of the spastic FDL. Similar findings were not evident in the slow-twitch fibers of the spastic SOL. Since the spastic condition causes increased muscular activity as a result of more rapid and prolonged nerve impulse firing, these findings reinforce the idea that a muscle fiber's oxidative capabilities are a function of its activity.     

去神经对快,慢肌纤维肌球蛋白ATPase影响的组织化学观察

本文用组织化学方法观察了豚鼠比目鱼肌(SOL)和腓骨第三肌(PT)在去神经后其快、慢纤维肌球蛋白ATPase特性的变化。在正常肌肉中Ⅰ型(慢)纤维和Ⅱ型(快)纤维分别具有酸和碱稳定ATPase活性。慢纤维在去神经后出现了碱稳定ATPase活性,而快纤维则无明显变化。结果表明,只有慢纤维的肌球蛋白ATPase特性才与神经支配有关。     

Myosin isozymes in normal and cross-reinnervated cat skeletal muscle fibers

Immunocytochemical characteristics of myosin have been demonstrated directly in normal and cross-reinnervated skeletal muscle fibers whose physiological properties have been defined. Fibers belonging to individual motor units were identified by the glycogen-depletion method, which permits correlation of cytochemical and physiological data on the same fibers. The normal flexor digitorum longus (FDL) of the cat is composed primarily of fast-twitch motor units having muscle fibers with high myosin ATPase activity. These fibers reacted with antibodies specific for the two light chains characteristic of fast myosin, but not with antibodies against slow myosin. Two categories of fast fibers, corresponding to two physiological motor unit types (FF and FR), differed in their immunochemical response, from which it can be concluded that their myosins are distinctive. The soleus (SOL) consists almost entirely of slow-twitch motor units having muscle fibers with low myosin ATPase activity. These fibers reacted with antibodies against slow myosin, but not with antibodies specific for fast myosin. When the FDL muscle was cross-reinnervated by the SOL nerve, twitch contraction times were slowed about twofold, and motor units resembled SOL units in a number of physiological properties. The corresponding muscle fibers had low ATPase activity, and they reacted with antibodies against slow myosin only. The myosin of individual cross-reinnervated FDL muscle units was therefore transformed, apparently completely, to a slow type. In contrast, cross-reinnervation of the SOL muscle by FDL motoneurons did not effect a complete converse transformation. Although cross-reinnervated SOL motor units had faster than normal twitch contraction times (about twofold), other physiological properties characteristic of type S motor units were unchanged. Despite the change in contraction times, cross-reinnervated SOL muscle fibers exhibited no change in ATPase activity. They also continued to react with antibodies against slow myosin, but in contrast to the normal SOL, they now showed a positive response to an antibody specific for one of the light chains of fast myosin. The myosins of both fast and slow muscles were thus converted by cross-reinnervation, but in the SOL, the newly synthesized myosin was not equivalent to that normally present in either the FDL or SOL. This suggests that, in the SOL, alteration of the nerve supply and the associated dynamic activity pattern are not sufficient to completely respecify the type of myosin expressed.     

Skeletal muscle adaptation in rats flown on Cosmos 1667

Seven male Wistar rats were subjected to 7 days of weightlessness on the Soviet biosatellite Cosmos 1667. Muscle histomorphometry and biochemical analyses were performed on the soleus (SOL) and extensor digitorum longus (EDL) of flight rats (group F) and compared with data from three groups of terrestrial controls: one subjected to conditions similar to group F in space except for the state of weightlessness (group S) and the others living free in a vivarium (V1, V2). Relative to group V2 (its age and weight-matched control group), group F showed a greater decrease of muscle mass in SOL (23%) than in EDL (11%). In SOL a decrease in the percentage of type I fibers was counterbalanced by a simultaneous increase in type IIa fibers. The cross-sectional area of type I fiber was reduced by 24%. No statistically significant difference in capillarization and enzymatic activities was observed between the groups. In EDL a reduction in type I fiber distribution and 3-hydroxyacyl-CoA-dehydrogenase activity (27%) occurred after the flight. The small histochemical and biochemical changes reported suggest the interest in studying muscular adaptation during a flight of longer duration.     

Structural and functional responses to prolonged hindlimb suspension in rat muscle

The purpose of this study was to investigate alterations in structural and functional properties in the soleus (SOL) and extensor digitorum longus (EDL) muscles of rats after 1, 2, and 5 wk of tail suspension. Maximal O2 uptake was 19% lower after 5 wk suspension. Loss of muscle mass was greater in SOL (63%) than in EDL (22%) muscle. A reduction of type I distribution was accompanied by an increase of intermediate fiber subgroups (int I in SOL, int II in EDL). The cross-sectional area of all three fiber types was reduced by hypokinesia. The decrease in capillaries per fiber in SOL was greater than the decrease in citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities after 5 wk. No alteration in lactate dehydrogenase activity was noted. In EDL, no changes in fiber area, capillarization, and enzymatic activities occurred. Energy charge remained unchanged (0.91) whatever the muscle. These results suggest that type I fibers showed an earlier and greater susceptibility than type II fibers to suspension which is also accompanied by a decreased aerobic capacity.     

Analysis of Rat Hindlimb Muscle Proteins by Two-Dimensional Gels Following Spinal Cord Injury

Proteins from extensor digitorum longus (EDL), plantaris (PLN), and soleus (SOL) muscles of adult, female rats were examined by high resolution two-dimensional gel electrophoresis up to 4 weeks following spinal cord transection. The electrophoretograms were analyzed by computer imaging and densitometry. Reproducible and significant changes in the relative concentrations of several proteins in each muscle type were detected. Whereas changes involving the largest number of proteins were observed in SOL, changes in EDL and PLN were also detected. In SOL, approximately 50% of the altered proteins increased in concentration and the remaining decreased: Actin and myosin light chains LCF-1 and LCF-2 were among those proteins whose concentrations increased, whereas myosin light chains LCS-1 and LCS-2 were among those proteins whose concentrations decreased. The present findings regarding the reversal in myosin light chain composition provide biochemical support for previously published data on changes in contractile properties of muscles following spinalization. In EDL, the relative concentration of only one protein was elevated in a time-dependent manner. The concentrations of two protein species in PLN were increased following cord transection. These findings provide new biochemical markers on the effects of spinal cord on gene expression in specific hindlimb skeletal muscles.     

Myosin subunits and contractile properties of single fibers from hypokinetic rat muscles

The effects of prolonged hypokinesia on the contractile properties and myosin isozymes of single fibers from the synergistic fast-twitch plantaris (PL) and slow-twitch soleus (SOL) skeletal muscles of adult rats were studied after 28 days of hindlimb suspension. There was a 31% increase in the mean maximal velocity of unloaded shortening (Vmax) among fibers from SOL with no change in the mean Vmax of fibers from PL after suspension. The myosin heavy and light chain (MHC and MLC) composition of bundles and the MHC composition of single fibers from control and suspended muscles were examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There was a marked increase in the relative amount of fast-type MHC's in hypokinetic SOL and a smaller increase in the amount of fast-type MHC's in the PL. Relatively minor changes occurred in the MLC's during hypokinesia. As Vmax increased among individual fibers from control and suspended muscles, the relative amount of fast-type MHC's increased. The results demonstrate that the myosin isozyme composition of skeletal muscle, especially the heavy chains, is altered during hypokinesia, and this finding provides an explanation for changes in Vmax of rat single muscle fibers under the same conditions.     

Enhanced neurally evoked responses and inhibition of norepinephrine reuptake in rat mesenteric arteries after spinal transection

In patients with high thoracic spinal lesions that remove most of the central drive to splanchnic preganglionic neurons, visceral or nociceptive stimuli below the lesion can provoke large increases in blood pressure (autonomic dysreflexia). We have examined the effects of T4 spinal transection on isometric contractions of mesenteric arteries isolated from spinalized rats. Nerve-evoked contractions involved synergistic roles for norepinephrine and ATP. At 7 wk after spinal transection, responses to perivascular stimulation at 1-5 Hz were enhanced fivefold, whereas the alpha1-adrenoceptor antagonist prazosin (10 nM) produced a twofold larger reduction in contraction (to 20 pulses at 10 Hz) than in unoperated controls. In contrast, the reduction in nerve-evoked contractions by the P2-purinoceptor antagonist suramin (0.1 mM) and the responses to the P2-purinoceptor agonist alpha,beta-methylene ATP or to high K+ concentration did not greatly differ between groups, indicating that arteries from spinalized rats were not generally hyperreactive. Sensitivity to the alpha1-adrenoceptor agonist phenylephrine was enhanced in arteries from spinalized rats, and the difference from controls was abolished by the norepinephrine uptake blocker desmethylimipramine. Sensitivity to the alpha1-adrenoceptor agonist methoxamine, which is not a substrate for the neuronal norepinephrine transporter, was similar among the groups. Thus the increased neurally evoked response after spinal transection appeared to be due to a reduction in neuronal uptake of released norepinephrine, a mechanism that did not explain the enhanced response of tail arteries after spinal transection that we previously reported. The findings provide further support for potentiated neurovascular responses contributing to the genesis of autonomic dysreflexia.     

Effects of beta 1- vs. beta 1- beta 2-blockade on training adaptations in rat skeletal muscle

The effect of selective vs. nonselective beta-blockade on fast-twitch [extensor digitorum longus (EDL)] and slow-twitch [soleus (SOL)] muscle enzyme activities following endurance training were characterized. Citrate synthase (CS), lactate dehydrogenase (LDH), and beta-hydroxyacyl-CoA dehydrogenase (HAD) activities were compared in SOL and EDL muscles of trained (T), metoprolol-trained (MT), propranolol-trained (PT), and sedentary (C) rats. Following 8 wk of treadmill running (1 h/day, 5 days/wk at approximately 30 m/min), LDH activity was depressed approximately 20% (P less than 0.05) in both SOL and EDL in only the PT rats, indicating inhibition of beta 2-mediated anaerobic glycolysis. EDL CS activity was similarly elevated in all three trained groups compared with sedentary controls. In SOL muscle, however, a drug attenuation effect was observed so that CS activity was increased only in the T (P less than 0.01) and MT (P less than 0.05) groups. HAD enzyme activity was increased somewhat (P less than 0.10) in SOL muscle in only the T group, but more so (P less than 0.05) in EDL in all three trained groups. The above findings suggest a training-induced selectivity effect not only with respect to beta 1-vs. beta 1-beta 2-blockers, but also with respect to muscle fiber type.     

Effects of β-hydroxy-β-methylbutyrate treatment in different types of skeletal muscle of intact and septic rats

β-Hydroxy-β-methylbutyrate (HMB) is a leucine metabolite that may have a positive effect in protein catabolic conditions. Therefore, we hypothesized that HMB treatment could attenuate the sepsis-induced protein catabolic state. The aims of our study were to elucidate the effect of HMB in healthy and septic animals and to evaluate the differences in the action of HMB in different muscle types. Intact and septic (5 mg endotoxin/kg i.p.) rats were administered with HMB (0.5 g/kg/day) or saline. After 24 h, extensor digitorum longus (EDL) and soleus (SOL) muscles were isolated and used for determination of total and myofibrillar proteolysis, protein synthesis, leucine oxidation, activity of cathepsins B and L, chymotrypsin-like activity, and expression of α-subunits of proteasome. Our results indicate that the catabolic state induced by the endotoxin treatment was caused both by increase in protein breakdown (due to activation of proteasome system) and by attenuation of protein synthesis. The EDL (muscle composed of white, fast-twitch fibers) was more susceptible to these changes than the SOL (muscle composed of red, slow-twitch fibers). The HMB treatment had no effect in healthy animals but counteracted the changes in septic animals. The action of HMB was mediated by attenuation of proteasome activity and protein breakdown, not by stimulation of protein synthesis. More pronounced effect of the HMB treatment on myofibrillar proteolysis was observed in the SOL.     

Effects of hindlimb suspension and androgen treatment on testosterone receptors in rat skeletal muscles

This study tested the specific and combined effects of testosterone treatment and hindlimb suspension (HS) on the properties of steroid receptors in skeletal muscle. Male rats were either administered weekly high doses of testosterone heptylate (10 mg x kg(-1)) or olive oil placebo, and were either tail-suspended or acted as controls. After 3 weeks of treatment, three muscles were excised from each animal, soleus (SOL), extensor digitorum longus (EDL), and plantaris. The results showed that the testosterone treatment was unable to minimise the HS-induced atrophy of skeletal muscle. As expected, HS altered the fibre-type composition of SOL muscles (-33% of type I, +188% and +161% of type IIa and intermediate fibres respectively, P < 0.01). No overall effect of treatment was detected on the fibre-type composition of either slow or fast-twitch muscles. Binding capacity determined by a radiocompetition technique was increased by HS, especially in SOL and EDL muscles (P < 0.01), while HS or steroid treatment decreased the affinity of the steroid receptors. The combination of HS and testosterone administration resulted in a decrease in binding capacity and affinity of steroid receptors in skeletal muscles. Steroid receptors in fast-twitch muscles exhibited a higher affinity than those in slow-twitch muscles, and it is suggested that it is likely that testosterone treatment is more effective in fast-twitch than in slow-twitch muscles. It was concluded that the lack of preventive effect of testosterone treatment on HS-induced SOL muscle atrophy could be explained by both a decrease in steroid sensitivity and the removal of mechanical factors.     

Changes in total fiber numbers of disused soleus muscle on rats

In this study, by use of technique that was modified from Morey method, we discussed the histological influence on the soleus muscle of the rats caused by disuse. This study is characterized by the calculating of total numbers of muscle fibers. ST (slow-twitch) and FT (fast-twitch) fibers in total muscular cross-sectional area were classified by their difference in intensity of staining of actomyosin adenosinetriphosphatase (myosin ATPase). During the experiment, average fiber diameter of ST and FT fibers declined when compared to control group (p less than 0.01). A 54% decrease in the total number of ST fibers was observed in the experimental group (p less than 0.01). Conversely, the total number of FT fibers increased to 362% of the control value (p less than 0.01). These results of the changes evoked in ST and FT fibers indicate 34% decrease in total muscular cross-sectional area, and showed that muscular function shifted toward a faster muscle in disused soleus muscle.     

Biochemical and physiological changes in overloaded rat fast- and slow-twitch ankle extensors

The rat soleus (SOL) or medial gastrocnemius (MG) were chronically overloaded by removing their major synergists bilaterally. After 12-14 wks the overloaded SOL (OS) and overloaded MG (OMG) muscles had approximately 50% greater cross-sectional areas (CSA) than the controls. Maximum twitch (Pt) and tetanic (Po) tensions were approximately 46% larger in the OS compared with the normal SOL. The OMG produced 10 and 37% higher Pt and Po, respectively. Specific tension (Po/CSA) was not altered in either group (P greater than 0.05). Contraction times and half-relaxation times were unchanged. Myofibrillar and myosin ATPase specific activities indicated a shift toward that resembling a slower muscle in both the OS and the red portion but not the white portion of the OMG. Generally, markers of glycogen metabolism were reduced (P less than 0.05) in the same muscle areas that showed reduced ATPase activity. These biochemical results were consistent with the apparent histochemical conversion of fibers from fast-twitch, glycolytic----fast-twitch, oxidative-glycolytic----slow-twitch, oxidative types in these muscle areas. These results suggest that overloading either a fast- or slow-twitch plantarflexor results in an increase in muscle mass and maximum tension and in metabolic shifts that generally resemble those observed in a slower muscle. Further, the degree of adaptation appears to be related to the initial fiber type composition of the muscle and/or of the muscle region.     

Repair of spinal cord transection and its effects on muscle mass and myosin heavy chain isoform phenotype.

A number of significant advances have been developed for treating spinal cord injury during the past two decades. The combination of peripheral nerve grafts and acidic fibroblast growth factor (hereafter referred to as PNG) has been shown to partially restore hindlimb function. However, very little is known about the effects of such treatments in restoring normal muscle phenotype. The primary goal of the current study was to test the hypothesis that PNG would completely or partially restore 1) muscle mass and muscle fiber cross-sectional area and 2) the slow myosin heavy chain phenotype of the soleus muscle. To test this hypothesis, we assigned female Sprague-Dawley rats to three groups: 1) sham control, 2) spinal cord transection (Tx), and 3) spinal cord transection plus PNG (Tx+PNG). Six months following spinal cord transection, the open-field test was performed to assess locomotor function, and then the soleus muscles were harvested and analyzed. SDS-PAGE for single muscle fiber was used to evaluate the myosin heavy chain (MHC) isoform expression pattern following the injury and treatment. Immunohistochemistry was used to identify serotonin (5-HT) fibers in the spinal cord. Compared with the Tx group, the Tx+PNG group showed 1) significantly improved Basso, Beattie, and Bresnahan scores (hindlimb locomotion test), 2) less muscle atrophy, 3) a higher percentage of slow type I fibers, and 4) 5-HT fibers distal to the lesion site. We conclude that the combined treatment of PNG is partially effective in restoring the muscle mass and slow phenotype of the soleus muscle in a T-8 spinal cord-transected rat model.     

Isolation of the cDNA encoding rat skeletal muscle myosin light chain kinase. Sequence and tissue distribution

A cDNA clone encoding skeletal muscle myosin light chain kinase (MLCK) was isolated from a rat skeletal muscle library using oligonucleotide probes. The total length of the rat skeletal muscle MLCK cDNA was 2823 base pairs with an open reading frame of 1830 base pairs. The deduced sequence of the 610-amino acid protein exhibited 96% amino acid identity to rabbit skeletal muscle MLCK in the carboxyl-terminal portion of the molecule, which contains the catalytic and the calmodulin-binding domains, and 58% identity in the amino-terminal region. Analysis of total rat mRNA revealed a single mRNA species of 3.4 kilobases that was unique to skeletal muscle. Further analysis of skeletal muscle tissue using fast-twitch glycolytic, fast-twitch oxidative glycolytic, and slow-twitch oxidative fibers isolated from rat leg revealed that the mRNA level for MLCK varied among the three fiber types. The results of kinase assays performed on the fibers showed that MLCK activity levels paralleled the MLCK mRNA levels found in each of the three types of skeletal muscle fibers studied. Fast-twitch oxidative glycolytic (gastrocnemius red) and slow-twitch oxidative (soleus) exhibited 60 and 13%, respectively, of the enzymatic activity present in fast-twitch glycolytic (gastrocnemius white) fibers.     

Cellular marker of myofiber activity for ankle flexor and extensor under conditions of rat hindlimb suspension

We supposed that the triglyceride content might be used as a cellular marker of muscle fiber activity and for the first time analyzed the triglyceride content in the fast- and slow-twitch muscle fibers of m. soleus and m. tibialis anterior under conditions of 7-day rat hindlimb suspension. Although the hindlimb suspension led to decrease of triglyceride content in the fast-twitch fibers of m. soleus and slow-twitch fibers of m. tibialis anterior, these differences were not significant. In spite of this the obtained data do not contradict our initial hypothesis.