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.

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.

[Ultrastructure of spindles in m. soleus of rats after repeated simulation of the weightlessness effects].

Postponed for a long time repeated simulation of the weightlessness effects in rats by tail-suspension increases in the amount of intrafusal muscle fibers in m. soleus spindles, reflecting presumably elevation of the sensitivity of mechanoreceptors.

[The absence of support loading on the rat m. soleus leads to an increase in the number of intrafusal muscle fibres in muscle spindles].

The ultrastructure of muscle spindles (incapsulated mechanoreceptors of stretch of extrafusal muscle fibres) of m. soleus in adult Wistar rats after repeated unloading of support on hind limbs with preservation of support loading on fore limbs has been studied by transmissing electron microscopy. It was shown that, along with muscle spindles with the ordinary number of intrafusal muscle fibres (four), m. soleus contains spindles with an increased number of intrafusal fibers (five to six). It was assumed that the increase in the number of intrafusal muscle fibers is due to the proliferation of their satellite cells.

[Ultrastructure of muscle spindles (Mechanoreceptors) of Rat m. soleus after support unloading and its combination with hypergravity]. / Ul'trastruktura myshechnykh vereten (mekhanoretseptorov) m. soleus krysy posle opornoi razgruzki i pri ee sochetanii s vozdeistviem gipergravitatsii.

We used electron microscopy to evaluate the effect of support unloading of m. soleus in adult Wistar rats (restrained in an antiorthostatic posture for 23-24 h/day within 24 days) on the ultrastructure of the intrafusal fibers and motor neuromuscular junctions of the muscle spindles, as well as the efficiency of intermittent hypergravity (+2Gz; 1 h/day for 19 days in a centrifuge in hypokinetic cages) as a countermeasure used in conditions of support unloading of this muscle. In the absence of support on the hind limbs, most of intrafusal fibers of m. soleus preserved the typical ultrastructure, while the axon terminals of the neuromuscular junctions accumulated a lot of synaptic vesicles (including large vesicles); the coated vesicles were absent due to unloading of the muscle and its muscle spindles (no contractions of the intrafusal fibers). A short-term effects of hypergravity at the background of support unloading of m. soleus mostly induced static loading of the muscle inducing different responses of the intrafusal fibers in different regions of the muscle spindles: local lysis of myofilaments was observed in single intrafusal fibers of the equatorial and intracapsular motor regions, while myofibrils remained intact in most fibers in the intra- and extracapsular regions of the spindles. The revealed adaptive response of the intrafusal fibers is, on the one hand, due to their specific innervation and ultrastructure and, on the other hand, to positive effect of hypergravity on the motor and extracapsular regions of the muscle spindles. Hypergravity decreased the number of synaptic vesicles and induced appearance of the coated vesicles in the axon terminals of the neuromuscular junctions of the intrafusal fibers in the animals restrained in an antiorthostatic posture (support unloading of m. soleus), which is due to increased functional load of the muscle. The ultrastructure of the muscle fibers adequately reflected the functional status of the postural m. soleus both during support unloading and support unloading combined with hypergravity load.

[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 need for a review of the procedure for the preventive vaccination of researchers working with Rickettsia prowazekii]. / Neobkhodimost' peresmotra taktiki profilakticheskoi vaktsinatsii sotrudnikov, rabotaiushchikh s Rickettsia prowazekii.

The analysis of the results of prolonged observations on the prophylactic immunization of employees working with R. prowazekii is presented. The necessity of the differentiated approach to the determination of the immunization schedule and the choice of vaccine is shown. The presence of specific antibodies (Ab) and the level of their titers have been found to be related to the degree of anti-infectious protection. The following characteristics indicate the presence of profound immunological transformation in vaccinees: complement-fixing Ab in titers 1:10 and more and/or immunofluorescent Ab in titers not below 1:180, Ab to protein in the hemagglutination test in titers not below 1:1000. These specific Ab and the level of their titers can be registered after the second injection of live combined typhus vaccine E and the third injection of chemical typhus vaccine. Cases of laboratory infection and their relationship to the character of immunization and the intensity of contacts with R. prowazekii virulent strains are discussed. Attention is drawn to the strict observance of professional safety rules.

The effect of increased functional load on the activation of satellite cells in the skeletal muscle of adult rats.

The comparison of the number of satellite cells in the fast oxidative glycolytic muscle fibers of m. quadriceps femoris in males of normal Wistar rats aged 16-17 weeks (5 animals) and rats trained for endurance (5 animals) was made. After six weeks of treadmill running at a speed of 35 m/min in an increasing regimen, the number of satellite cells in trained animals (9.59 +/- 1.09%) increased over 2.5-fold in comparison to controls (3.41 +/- 0.26%) within 24 hours. At the ultrastructural level complete and focal injuries of some muscle fibers and the partial denervation of individual muscle fibers were recorded in trained rats. It was proposed that the focal functional denervation of muscle fibers could be one of the factors for the activation of satellite cells in endurance exercise. Some trained rats demonstrated small groups of extra- and perisynaptic satellite cells under the basal membrane of muscle fibres, partial detachment of satellite cells from the surface of muscle fiber and presence in the interstitial space cell containing filaments.