CYTOLOGICAL LOCALIZATION OF CHOLINESTERASE IN CULTURED SKELETAL MUSCLE CELLS

The location of acetyl and butyryl thiocholinesterase activity was studied in cultured chick embryo skeletal muscle cells which were growing without being innervated. Muscle cells in all three stages of development, i.e., the single myoblast, the plurinucleated myoblastic strap, and the multinucleated myocytic strap, showed sites of thiocholinesterase activity as small brown granules located diffusely in the cytoplasm and accentuated in the perinuclear areas. In the well differentiated myocytic straps, thiocholinesterase was localized along the Z lines. No enzyme activity was found at the sarcolemma or in the nuclei. No thiocholinesterase-containing motor end-plate structures were found in any stage of development.