Influence of the SERCA Activity on Rat’s Soleus Contractile Properties during Functional Unloading

Abstract

Dysfunction of skeletal muscles and their atrophy during unloading are accompanied by excess calcium accumulation in the myoplasm of muscle fibers. We hypothesized that calcium accumulation may occur, among other reasons, due to inhibition of SERCA activity under muscle unloading. In this case, the use of a SERCA activator will reduce the calcium level in the myoplasm and prevent the consequences of unloading. Male Wistar rats were divided into 3 groups: vivarium control with placebo administration (C, n = 8), 7-day suspension group with placebo administration (7HS, n = 8) and 7-day suspension group with intraperitoneal administration of SERCA CDN1163 activator (50 mg/kg (7HS + CDN), n = 8). One m. soleus of each rat was frozen in liquid nitrogen, the second was tested for functional properties. In the 7HS group, increased soleus fatigue was found in the ex vivo test, a significant increase in mRNA and the number of fast muscle fibers, an increase in the level of calcium-dependent CaMK II phosphorylation and the level of tropomyosin oxidation, as well as a decrease in the content of mitochondrial DNA and protein. All these changes were prevented in the SERCA CDN1163 activator group. Conclusion: 7-day SERCA activator administration does not delay of soleus atrophy, but prevents the development of its fatigue, probably by preventing a decrease in the number of type I fibers and markers of mitochondrial biogenesis.