Localization of the Ca(2+)-binding S100A1 protein in slow and fast skeletal muscles of the rat.

The distribution of S100A1 in rat soleus and EDL muscles was studied immunocytochemically at the ultrastructural level using immunogold as marker. Antigens were localized mainly in myofibrils at all levels of the sarcomere. Immunogold particles along myofibrils were not uniformly distributed. The highest density of particles was found at Z-lines. An increase in particle density was observed in the middle of half A-bands in EDL and in the middle of half I-bands in the soleus. Antigen sites were also present at M-lines and at distinct locations of the sarcoplasmic reticulum.