ОТ АКТИВНОСТИ К БЕЗДЕЙСТВИЮ И СНОВА К АКТИВНОСТИ. СИГНАЛЬНЫЕ ПРОЦЕССЫ В ПОСТУРАЛЬНОЙ МЫШЦЕ В ПЕРЕХОДНЫЙ ПЕРИОД

Abstract

Experiments with tail-suspended rats exposed to Kepler's parabolic flight and human subjects in dry immersion showed repeatedly decreases, sometimes to the point of full inhibition, of the soleus m. electrical activity. Stopping the activity, closely resembling the temporal physiological rest that in rat's m. soleus is normally 8-10 hours a day, is much longer in experiments and can be characterized as a state of inactivity. Already after 24 hours of inactivity, expression of key muscle ubiquitin Е3 ligases increases with parallel reductions in protein synthesis and translational capacity. Expression of the slow isoform of myosin heavy chains reduces also. Purpose of the review is to summarize the data on dynamics of molecular events in postural m. soleus of the mammal after cessation of its contractile activity. Changes in the complex of signaling pathways in the transitional period are triggered by a group of molecular messengers which are directly dependent on the contractile activity. Established was the function of increasing ATP concentration and ensuing reduction in phosphorylation of АМP-activated protein kinase (АМPК), as well as expression of slow myosin, regulators of mitochondria and ribosomes biogenesis and resting membrane potential at the initial stage of muscle inactivity. ATP-dependent processes contribute to NO reduction and Ca2+ions accumulation in muscle fibers. Changes in these messengers precisely underlie the subsequent atrophic developments, transformation of myosin phenotype, muscle fiber atony and mitochondrial dysfunction. At the same time, due to still not clearly understood changes in excitability of spinal motoneurons, within three day of inactivity the postural muscle demonstrates spontaneous activity with a gradually growing amplitude of electromyographic signals. Results of the investigations of signal processes in the postural muscle during the transition from activity to inactivity and back to autonomic activity suggest difference and nonuniformity and nonlinearity of these processes and change of mechanisms driving the destructive events.