Expression of SERCA2a is not regulated by calcineurin or upon mechanical unloading in skeletal muscle regeneration.

This study investigates to what extent the expression of the slow myosin heavy chain (MyHCI) isoform and the slow type sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) isoform are co-regulated in fibers of regenerating skeletal soleus muscle. Both overexpression of cain, a calcineurin inhibitor, or partial tenotomy prevented the expression of MyHCI but left SERCA2a expression unaffected in fibers of regenerating soleus muscles. These data complement those from different experimental models and clearly show that the expression of MyHCI and SERCA2a--the major proteins mediating, respectively, the slow type of contraction and relaxation--are not coregulated in regenerating soleus muscle.

The calcineurin activity and MCIP1.4 mRNA levels are increased by innervation in regenerating soleus muscle.

The level of active subunit of calcineurin and the calcineurin (Cn) enzyme activity are increased in innervated but not in denervated slow type regenerating skeletal soleus muscle. These nerve-dependent increases were not accompanied by similar increases in the mRNA levels. The changes in the mRNA level of the modulatory calcineurin interacting protein, MCIP1.