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.

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 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.

Effect of glucocorticoids on contractile apparatus of rat skeletal muscle.

Skeletal muscles which have a high oxidative potential are less sensitive to the catabolic action of dexamethasone. In fast-twitch white muscles, where the oxidative capacity is low, the alkaline proteinase activity as well as the rise in the number of lysosomes was more pronounced. It seems that the glucocorticoid-caused myopathy is a result of elevated degradation of contractile proteins. This process of degradation of contractile proteins begins in the myosine filaments and then spreads to the thin filaments and the z-line.

Effect of muscular activity on the turnover rate of actin and myosin heavy and light chains in different types of skeletal muscle. I. Changes in the turnover rate of myosin and actin during and after single-bout physical activity.

During a single-bout of 6-h swimming, myosin heavy chain (HC) and actin in m. gastrocnemius turned over more slowly than they did in the pre-exercise period, whereas the turnover rate of myosin light chain (LC) increased; 48 h after swimming, actin and myosin HC had a significantly higher turnover rate, but the turnover rate of myosin LC remained at the pre-exercise level. Exercise caused a remarkable decrease in the incorporation of the 14C leucine into actin and myosin HC, but an increase in the incorporation into myosin LC. An elevation of the synthesis rate of actin and myosin HC was observed 48 h after exercise. Myofibrillar proteinase activity at alkaline pH reached its maximum level during exercise, but the same was observed for the proteolytic activity at acid pH 6 h and at neutral pH 24 h after exercise.