Exercise myopathy: changes in myofibrils of fast-twitch muscle fibres.

The purpose of the present study was to determine the relationships between the changes of myofibrils in fast-twitch oxidative-glycolytic (type IIA) fibres and fast-twitch glycolytic (type IIB) muscle fibres, protein synthesis and degradation rate in exercise-induced myopathic skeletal muscle. Exhaustive exercise was used to induce myopathy in Wistar rats. Intensity of glycogenolysis in muscle fibres during exercise, protein synthesis rate, degradation rate and structural changes of myofibrils were measured using morphological and biochemical methods. Myofibril cross sectional area (CSA) in type IIA fibres decreased 33% and type IIB fibres 44%. Protein degradation rate increased in both type IIA and IIB fibres, 63% and 69% respectively in comparison with the control group. According to the intensity of glycogenolysis, fast oxidative-glycolytic fibres are recruited more frequently during overtraining. Myofibrils in both types of fast-twitch myopathic muscle fibres are significantly thinner as the result of more intensive protein degradation. Regeneration capacity according to the presence of satellite cells is higher in type IIA fibres than in type IIB fibres in myopathic muscle.

Muscle protein turnover in endurance training: a review.

There has been much debate about skeletal muscle capacity to adapt to long-lasting endurance exercise. Exercise in the aerobic zone of metabolism does not result in hypertrophy of skeletal muscle fibres but increases their oxidative capacity. The duration and intensity of an exercise session determines the time period of depressed muscle protein synthesis and increased degradation rate during the recovery period after exercise. Protein turnover characterizes the renewal processes of muscle proteins and the functional capacity of muscle. The turnover rate of myofibrillar proteins is slow in comparison with mitochondrial proteins and depends on the oxidative capacity of muscle fibres. The turnover rate of myofibrillar proteins in the same muscle is different and is also different within the myosin molecule between myosin heavy and light chain isoforms. The turnover rate of muscle proteins in endurance training shows the adaptation of skeletal muscle to long-lasting exercise via remodelling of muscle structures. Adaptational coordination between myofibrillar and mitochondrial compartments shows the physiological role and adaptational capacity of skeletal muscle to endurance training. It is challenging to use muscle protein turnover for the purposes of monitoring the training process of endurance athletes, optimizing training programs and preventing overtraining.

Extracellular matrix and myofibrils during unloading and reloading of skeletal muscle.

The aim of the study was to elucidate the effect of unloading and reloading on the collagen expression and synthesis rate of myofibrillar proteins in fast-twitch (FT) muscle in relation to changes in muscle strength and motor activity. Northern blot analysis was used for testing the specificity of cDNA probes and protein synthesis rate was measured according to incorporation of radioactive leucine into different protein fractions. Unloading depresses collagen type I and III (p<0.001), type IV (p<0.05) and reloading enhances collagen expression in fast-twitch skeletal muscle in comparison with unloading. Enhanced expression of matrix metalloproteinase-2 continued during the first week of reloading (p<0.01) and tissue inhibitor of metalloproteinase-2 during reloading (p<0.05). Changes in collagen expression in FT muscle are in good agreement with changes in myofibrillar protein synthesis during unloading and reloading. In conclusion alterations in extracellular matrix and myofibrillar apparatus in FT skeletal muscle are related to changes in muscle strength and motor activity, are significant in exercise training and determination of recovery periods in the training process as well as in athletes' rehabilitation.

Myosin heavy chain pattern in the Akhal-Teke horses.

This study investigates the myosin heavy chain (MyHC) isoform composition in the gluteus medius muscle of the Akhal-Teke horses using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). Fifteen horses aged between 1.5 and 23.5 years were used in this study and divided into three age groups: 1.5 to 4 (n = 6), 9 to 13 (n = 5) and 18.5 to 23.5 years (n = 4). The average content of the MyHC I isoform was 11.72 ± 1.07% (variation between individuals: 7.09% to 20.14%). The relative content of the MyHC IIa and IIx isoforms was subsequently 38.20 ± 1.46% (30.73% to 48.78%) and 50.07 ± 1.10% (43.8% to 56.78%) from the total MyHC. The MyHC pattern in the skeletal muscles of the Akhal-Teke horses shows that the muscles of these horses have a high capacity both for endurance and speed.

Structural rearrangements in contractile apparatus and resulting skeletal muscle remodelling: effect of exercise training.

This review briefly summarizes studies that examine fast- and slow-twitch skeletal muscles and the ultra- and molecular structure of fibre types, including intrafusal fibres, during adaptation to exercise training. Adaptation capability of skeletal muscle to different types of exercise training depends on rearrangements in the contractile apparatus, mitochondria, other fibre organelles and neuromuscular junctions. Skeletal muscle functional capacity depends on structural changes in fibre organelles and is related to higher centres of motor control as the adaptation process needs information about muscle length and speed of contraction at any time during the training process. The renewal of the contractile apparatus in skeletal muscle during exercise training supports the qualitative remodelling of muscle so that the muscle contraction is better suited to the new conditions. The effectiveness of metabolic processes in new conditions depends on the structural-functional relationships between the energy system and contractile machinery in muscle fibres.

Changes in fast-twitch muscle oxidative capacity and myosin isoforms modulation during endurance training.

AIM: The purpose of this study was to investigate the effect of endurance training on changes in myosin heavy (MyHC) and light (MyLC) chains expression, their turnover rate in fast-twitch (FT) skeletal muscles, and relations with changes in contractile proteins degradation rate and muscle oxidative capacity. METHODS: Wistar rats were run at 35 m/min for 6 weeks (from 10 min to 60 min per day, from 1.8 kJ to 7 kJ per training session and power of work was 1.5 W). The FT muscles were used for measurement of myosin isoforms and oxidative capacity. Double isotope method ((3)H/(14)C) was used. RESULTS: During endurance training in plantaris and extensor digitorum longus (EDL) muscles the relative content of MyHC IIb isoform decreased while there was an increase in the relative content of MyHC IIa and IId isoforms. MyLC 3(fast) isoform increased in FT muscles. Degradation rate of MyHC isoforms increased during endurance training simultaneously with the increase of contractile proteins degradation and increase of cytochrome aa3 content in FT muscles. Endurance training increased MyHC I, IIa and IId isoform turnover rate, whereas MyHC IIb and MyLC isoforms turnover rate did not change significantly. CONCLUSIONS: Adaptation of FT skeletal muscles to endurance training shows coordination between increase in oxidative capacity and faster turnover rate of MyHC isoforms in contractile apparatus. FT muscles show high potential of recruitment in endurance training.

The profile and distribution of myosin heavy chain isoforms in middle-aged sedentary persons.

AIM: Human lifestyle has drastically changed during the past century as the share of physical work in daily life has decreased. The purpose of the present study was to examine the distribution of myosin heavy chain (MHC) isoforms in middle-aged sedentary persons, to compare the proportion of MHC isoforms of middle-aged and young sedentary persons and to demonstrate the effect of physical activity of MHC isoforms in middle-aged sedentary persons. METHODS: Eighty-nine middle-aged sedentary and 13 young sedentary persons volunteered for the study. Thirty middle-aged sedentary subjects participated in strength-conditional exercise program during 9 months. Vertical jumping height and maximal anaerobic work capacity were measured. Muscle samples were taken from vastus lateralis muscle. MHC isoform composition was determined by SDS-PAGE. RESULTS: Variation of MHC I and MHC IIa isoforms in middle-age sedentary persons demonstrated normal distribution. Significant differences of MHC isoform proportions between middle-aged and young sedentary participants were not observed. The proportion of MHC IIx decreased significantly after the exercise period that significantly improved the maximal anaerobic power and jumping height of participants. CONCLUSIONS: Normal distribution illustrated the proportion of MHC I and MHC IIa isoforms in 89 middle-aged sedentary persons while significant differences of MHC isoforms proportion between young and middle-aged sedentary persons were not observed. Even small increase of physical activity improved physical performance and decrease the MHC IIx proportion of middle-aged sedentary persons. Physically active lifestyle in middle age, when age-related changes have not started yet, may delay age-related changes in skeletal muscle.

Endurance training: volume-dependent adaptational changes in myosin.

The purpose of this study was to find the effect of different endurance training volumes on the composition and turnover of myosin. Sixteen-week-old male rats of the Wistar strain were divided into three different volume-based training groups. Changes in myosin heavy chain (MyHC), myosin light chain (MyLC) isoforms' composition, their synthesis rate, as well as myosin binding C-protein synthesis rate, and muscle protein degradation rate were measured. In slow-twitch (ST) soleus (Sol) muscle MyHC I isoform relative content increased and MyHC IIa isoform decreased during excessive increase in the volume of endurance training (ET). In plantaris (Pla) muscle excessive increase in ET volume decreased MyHC I and IIb isoforms, and increased MyHC IIa and IId relative content. In extensor digitorum longus (EDL) muscle the relative content of MyHC IId isoform increased during ET, but excessive increase in training volume decreased it. In Pla muscle the relative content of MyLC 1 (slow) isoform decreased during ET, but excessive increase in ET volume decreased the relative content of MyLC 3 (fast) isoform in both fast-twitch (FT) muscles. Decrease in MyHC and myosin binding C-protein synthesis rate in Pla muscle had significant correlation with ET volume (r = - 0.537, p < 0.05 and r = - 0.727, p < 0.001 subsequently). MyHC I and IIb isoforms and MyLC 3 (fast) isoform in Pla muscle and MyHC IIb, IId and MyLC 3 (fast) isoforms in EDL muscle are the most sensitive to the increase in ET volume. Excessive increase in ET volume leads to a decrease in physical working capacity. The degradation of muscle protein increased during ET in all groups.

Composition and turnover of contractile proteins in volume-overtrained skeletal muscle.

The purpose of this study was to find the composition shift of myosin heavy chain (MyHC) isoforms in overtraining in fast- and slow-twitch skeletal muscles and different changes in MyHC isofom composition, synthesis and turnover rate between 4-week and 6-week overtraining. Male Wistar rats were randomly assigned to 4-week and 6-week endurance training, 4-week and 6-week overtraining groups. Plantaris (Pla), extensor digitorum longus (EDL), and soleus (Sol) muscles were studied. Daily excretion of 3-methylhistidine (3-MeHis) pool as an indicator for protein degradation increased in the 4-week and 6-week overtraining group to 4.04 +/- 0.21 and 4.32 +/- 0.23 %/day subsequently in comparison with the control group (2.16 +/- 14 %/day, p < 0.001). In Pla muscle MyHC I isoform synthesis rate was 33 200 +/- 2150 (after 6-week overtraining 27 100 +/- 1800, p < 0.05), IIa 32 600 +/- 2100; IId 27 300 +/- 1890 and IIb isoform 20 100 +/- 1600 (after 6-week overtraining 15 500 +/- 1400, p < 0.05) dpm/M leucine/min. Actin synthesis rate increased in fast-twitch muscles during 4- and 6-week overtraining, and in soleus muscle during 6-week overtraining. In EDL and Sol muscle MyHC isoform composition during 6-week overtraining did not change significantly. During the 6-week overtraining the relative content of MyHC I and IIb isoforms decreased and IIa and IId isoforms increased in Pla muscle. The initial increase of MyHC IIb isoform after 4-week overtraining shows the higher stability of this isoform in comparison with MyHC I isoform in fast-twitch muscles during high volume exercise.

The effect of mechanical loading on the MyHC synthesis rate and composition in rat plantaris muscle.

The aim of this study was to investigate the response of protein synthesis rate, particularly myosin heavy chain (MyHC) isoforms synthesis and the magnitude of its isoform transformation in fast-twitch plantaris muscle, to different modes of prolonged mechanical loading. Different protocols of mechanical loading were used: resistance training (RT), compensatory hypertrophy (CH) of m. plantaris after tenotomy of m. gastrocnemius and a combination of the two previous loadings (RT + CH). During the different modes of loading, plantaris muscle hypertrophy in RT group was approximately 10 %, CH approximately 40 % and CH + RT approximately 44 %. MyHC I and IID isoform synthesis rate increased in all experimental groups, as well as their relative content. MyHC IIA relative content decreased during RT and RT + CH and increased during CH. MHC IIB isoform relative content decreased in all experimental groups, but compared with CH in CH + RT MyHC IIB isoform content increased in plantaris muscle. These results demonstrate that different modes of mechanical loading resulted in the selective up- and down-regulation of MyHC isoforms in fast-twitch skeletal muscle. The synthesis rate and relative content of the two fastest isoforms of MyHC IIB and IID are regulated to different directions during mechanical loading.

[Ultrastructure of the neuromuscular junctions in the rat soleus muscle under varying gravity conditions]. / Ul'trastruktura nervnomyshechnykh soedinenii kambalovidnoi myshtsy (m. soleus) krysy pri izmenenii uslovii gravitatsii.

Changes in the ultrastructure of neuromuscular junctions have been considered as an index to adaptation of Wistar rats (whose pre- and postnatal ontogenesis proceeded on a centrifuge under constant rotation until the age of two months) to the hypergravity conditions (2G) and, then, to earth gravity (1G): on the 2nd and 15th days after centrifuge stoppage. The dynamic of synaptic vesicles was shown: their number increased at 2G and gradually decreased at 1G. Local damage of muscle fibers, partial separation of the motor axonal terminal from intrafusal fiber, and membrane twisting were noted at the increased gravity-dependent static load (2G). Neuromuscular junctions with signs of remodeling occurred more frequently in the experimental rats than in the control ones. It was proposed that adaptation of rats to 1G gravity after a prolonged sojourn under the hypergravity conditions (2G) was not completed within the studied period.

[Ultrastructure of type 2A extrafusal muscle fibers and intrafusal fibers of the muscle spindle (m. quadriceps femoris) from the adult rat after long-term swimming]. / Ul'trastruktura ékstrafuzal'nykh myshechnykh volokon tipa 2A i intrafuzal'nykh volokon myshechnogo veretena (m. quadriceps femoris) vzrosloi krysy posle prolongirovannogo plavaniia.

We compared the ultrastructure of type 2A extrafusal muscle fibers, the nuclear chain, and other intrafusal fibers of muscle spindle (muscle stretch mechanoreceptor) in adult rats after a prolonged swimming (5-10 h/day, 10 days). The Golgi apparatus was expressed moderately in type 2A extrafusal fibers and hypertrophied in the motor B zone of nuclear chain intrafusal fibers. Intense development of the Golgi apparatus in the nuclear chain intrafusal fiber appears to be related to glycogenolysis in the autophagous vacuoles, involvement in the lysosome activity, and plasma membrane renewal. "Recapitulation" of the mechanism of glycogen autophagy, which is observed in newborn rats during mobilization of glycogen from the liver and muscle, was demonstrated in adult rats under the influence of physical load in the nuclear chain and nuclear bag 2 intrafusal fibers and in type 2A extrafusal fibers. This is accounted for by a weak differentiation of the intrafusal muscle fibers: structurally, they are similar to myotubes and have specific features of blood supply and innervation. Individual features of experimental adult rats may also play a certain role.

[Ultrastructural characteristics of rat neuromuscular junctions after physical load]. / Ul'trastrukturnye kharakteristiki nervno-myshechnykh soedinenii krys posle fizicheskikh nagruzok.

It is interesting to ascertain the adaptive reaction of rat neuromuscular junctions (NMJ) of muscle fibers of different types to a chronic physical load. We examined ultrastructural changes in NMJ following both static load (pre- and postnatal ontogenesis of Wistar rats till a 2 month age took place under a constant rotation on the centrifuge at hypergravity conditions 2G), and after three kinds of dynamic loads (1/run on treadmill with a speed 35 m/min for 6 wks, 10-60 min/day; 2/swimmings, each 10 hrs/day for 10 days; 3/strength exercises on a vertical treadmill with load for 6 wks). Differences in NMJ reaction of muscle fibers of the same type to various loads were established. A low secretory activity of axonal terminals of type I muscle fibers of m. soleus was shown after the static load. The dynamic load (run) is accompanied with a high secretory activity of axonal terminals in m. soleus type I muscle fibers and of some axonal terminals of m. quadriceps femoris IIB type muscle fibers after strength exercises; the secretory activity of axonal terminals of m. quadriceps femoris IIA and IIB types muscle fibers is expressed in a lesser degree after swimming. The NMJ ultrastructure remodelling (terminal renewal) of type I muscle fibers of the 2 month old control rats increases after static and dynamic (run) loads. Some correlations between different kinds of physical load, muscle fiber type and the degree of NMJ ultrastructure transformation have been shown.

The effect of autografting on the myosin composition in skeletal muscle fibers.

The purpose of the study was to investigate the changes in myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following autotransplantation of extensor digitorum longus muscles. Muscles were grafted in "standard" and "nerve-intact" conditions. MHC and MLC isoforms were analyzed by sodium dodecyl sulphate gel electrophoresis. Changes in MHC isoforms 10, 30, and 60 days after grafting were similar in the "standard" and the "nerve-intact" grafts. In contrast to MHC, changes in MLC were different in the 10th day groups, but the same in the 30th day groups. Sixty days after grafting the content of MLC isoforms was the same as the control muscles. These data indicate that transient loss of functional innervation, even for a short time, has permanent effect on the composition of MHC but not MLC isoforms in regenerating skeletal muscle fibers.

Skeletal muscle and heart antioxidant defences in response to sprint training.

Although endurance training enhances the antioxidant defence of different tissues, information on the effect of sprint training is scanty. We examined the effect of sprint training on rat skeletal muscle and heart antioxidant defences. Male Wistar rats, 16-17 weeks old, were sprint trained on a treadmill for 6 weeks. Total glutathione levels and activities of glutathione peroxidase, glutathione reductase, glutathione S-transferase and superoxide dismutase in heart and various skeletal muscles were compared in trained and control sedentary animals. Lactate dehydrogenase and citrate synthase enzyme activities were measured in muscle to test the effects of training on glycolytic and oxidative metabolism. Sprint training significantly increased lactate dehydrogenase activity in predominantly fast glycolytic muscles and enhanced total glutathione contents of the superficial white quadriceps femoris, mixed gastrocnemius and fast-glycolytic extensor digitorum longus muscles. Oxidative metabolic capacity increased in plantaris muscle only. Compared with the control group, glutathione peroxidase activities in gastrocnemius, extensor digitorum longus muscles and heart also increased in sprint trained rats. Glutathione reductase activities increased significantly in the extensor digitorum longus muscle and heart. Glutathione S-transferase activity was also higher in the sprint trained extensor digitorum longus muscle. Sprint training did not influence glutathione levels or glutathione-related enzymes in the soleus muscle. Superoxide dismutase activity remained unchanged in skeletal muscle and heart. Sprint training selectively enhanced tissue antioxidant defences by increasing skeletal muscle glutathione content and upregulating glutathione redox cycle enzyme activities in fast and mixed fibre leg muscles and heart.