Effects of cyclosporine-A on rat soleus muscle fiber size and phenotype.

Purpose: Organ transplant patients treated with cyclosporine-A (CsA) often exhibit weight loss and muscle weakness. The cellular target of CsA, calcineurin, has been implicated in maintenance of muscle fiber size and in expression of the type I skeletal muscle phenotype. We hypothesized that CsA treatment would cause fiber atrophy, as well as increase type IIa myosin heavy chain (MHC) content and oxidative enzyme activities in the soleus muscle.