[Relationship between the ionic composition and functional activity of rat skeletal muscles].

Studies have been made on the relationship between the pattern of distribution of sodium and potassium ions in skeletal muscles of rats (tissue concentrations of ions, ionic selectivity of the tissue) and the level of functional activity of these muscles under experimental influences upon the motor system of the animals. It was shown that prolonged (20 days) effect of weightlessness during a cosmic flight (functional unloading of the motor apparatus) induces changes in tissue concentrations of Na+ and K+ (the increase of the former and the decrease of the latter) only in postural-tonic m. soleus, which accounts for antigravitational function in the organism. In m. phrenicus and m. plantaris no significant shifts in tissue concentrations of ions were detected. severe hypokinesia (30 days) in the laboratory, as well as denervation (30 days) considerably decrease tissue concentrations of K+ and increase that of Na+ in fast skeletal muscles; under the same conditions, slow m. soleus exhibits simultaneous changes in tissue concentrations of Na+ and K+, although these are less significant.