[Dynamics of calcium levels and changes SERCA content in muscle fibers of rats and Mongolian gerbils during hind limb unloadings of various duration].

In this study, it was shown that calcium levels in the fibers of m. soleus of Mongolian gerbils after one day of unloading increased four and a half times in comparison with the control. In rats, the situation differed: 2.8 times increase after the 1st day of hypogravity persisted until the 3rd day and then calcium levels slightly decreased to the 12th day. However, the base concentrations of calcium in the control group of gerbils were significantly lower than in control rats, thus there was larger shift of this parameter during the first day. Probably, this was the reason for an earlier start of the protein phenotype shift in gerbils: statistically significant increase in the number of fibers with "fast" SERCA isoforms was detected after one day of unloading and therefore slow-to-fast shift in myosin phenotype was observed on the 3rd day of unloading. The same changes in rat muscle could be detected only after the 7th and the 12th day, respectively. In both species, there was a tendency to restore their initial parameters to the 12th day but in gerbils it was much more intensive.