[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.

[Effect of increased functional activity of skeletal muscles on the turnover rate of heavy and light chains in myosin]. / Vliianie povyshennoi funktsional'noi aktivnosti skeletnykh myshts na skorost' obnovleniia tiazhelykh i legkikh tsepei miozina.

Incorporation of 14C-leucine into light chains (LC) of myosin was distinctly increased and into heavy chains (HC)--decreased during physical exercises. Within first six hours after the exercises synthesis of HC maintained at the reduced level, then it was gradually elevated and distinctly activated after 48 hrs rest. Incorporation of 14C-leucine into LC of myosin was unaltered at the post-exercise period. During swimming turnover of LC myosin was accelerated and after physical activity it maintained at the level of controls. The rate of HC myosin turnover was not distinctly altered both during physical activity and within the first day after the loading. The rate of HC myosin turnover was augmented within 48 hrs after exercises.

[Protein metabolism in the muscles after work]. / Belkovyi obmen v myshtsakh posle ikh raboty.

The 20-hr swimming increased the contants of protein, thyrosine and 3-methylhistidine (also per 1 g of protein) in skeletal muscle of rat within 2-24 hrs. A significant increase in 3-methylhistidine excretion followed this on the 2nd day of the recovery period. The revealed combination of changes suggests a simultaneous augmentation of both synthesis and disintegration of protein in muscles after their activity. Hence, the increased excretion of 3-methylhistidine during recovery period reflects an intensive renewal of the molecular content of proteins of actinomyosine complex. The 3-methylhistidine level in intestine increased only for a short time and seems not to contribute to the delayed increase in excretion of the amino acid.