SERCA isoform expression in paralyzed muscle

The influence of paralysis on the expression of sarco(endo)plasmic reticulum calcium ATPase (SERCA) pump isoforms in the rat soleus muscle was assessed. Paralysis was induced in rats via a complete mid‐thoracic spinal cord transection (ST). SERCA pump protein isoform expression in single muscle fibers was evaluated at 15 and 30 days post‐ST using immunohistochemistry and compared to myosin heavy chain (MyHC) isoform content. In control rats, ~60% of soleus fibers examined contained slow MyHC and SERCA isoforms, another ~25% contained slow MyHC and both fast and slow SERCA isoforms. The majority of the remaining fibers contained fast isoforms of MyHC and SERCA. Fifteen days after ST no fibers contained both slow MyHC and SERCA, ~60% contained slow MyHC and both SERCA isoforms, and ~25% contained fast and slow MyHC and SERCA isoforms. Thirty days after ST no fibers contained both slow MyHC and SERCA, ~30% contained slow MyHC and both SERCA isoforms, ~30% contained fast and slow MyHC and SERCA isoforms, ~20% contained both fast and slow MyHC and only fast SERCA isoforms, and ~20% contained just the fast isoforms of MyHC and SERCA. These data are consistent with a more rapid slow to fast transformation in SERCA than MyHC isoforms after paralysis and suggest that the cellular factors that direct transformations in SERCA isoform expression are distinct from those that direct transformations in MyHC isoform expression after paralysis. Supported by NIH GM53933.