[NFATc1 and slow-to-fast shift of myosin heavy chain isoforms under functional unloading of the rat m. soleus].

It was determined whether the content of NFATc1 (nuclear factor of activation of T cells) in the nuclear and cytoplasmic extracts is related to an increase in the content of fibers containing type IIa myosin heavy chains under gravitational unloading of m. soleus. It was found that three isoforms of NFATc1 with molecular masses of 140, 110, and 86 kDa are present in m. soleus. Under unloading, the translocation of 140 kDa NFATc1 into the nucleus, a decrease in the content of 110 kDa NFATc1 in the cytoplasmic extract of m. soleus, and an increase in the content of 86 kDa NFATc1 in the nuclear extract of m. soleus take place. The content of fibers containing type IIa myosin heavy chains under gravitational unloading increases. The increase in the level of 140 and 86 kDa NFATc1 in the nucleus is accompanied by a decrease in the percentage of fibers containing type I myosin heavy chains and an increase in the percentage of muscle fibers containing type IIa myosin heavy chains.