[Structural differences in the structure of the ciliary muscles in eyes of primates. A histochemical and...

The ciliary muscle of the primate eye was stained histochemically with enzymes used to differentiate fiber types in the skeletal muscle. Differences between the outer meridional section and the rest of the muscle were found with all enzymes. Staining for myosin-ATPase with acid and alkaline preincubation, as well as for lactate dehydrogenase (LDH), resulted in a stronger reaction in the meridional section, while the reticular and circular portions showed minor activities. In contrast, succinate dehydrogenase (SDH) revealed a stronger activity in the reticular and circular muscle cells. Ultrastructurally, the meridional muscle cells contained fewer mitochondria, but more myofibrils in the cytoplasm, while circular and reticular muscle cells showed just the opposite. Therefore, the cells of the meridional ciliary muscle section resemble in some respects the rapid type-II skeletal muscle fibers, and the circular und reticular muscle cells are comparable to the slow type-I fibers of the skeletal muscle.