Structure and macromolecular composition of the myotendineal junction. Histochemical, immunohistochemical and electron microscopic study of the rat calf muscles.

The macromolecular composition and ultrastructure of the myotendineal junction (MTJ) of slow-twitch (type 1) and fast-twitch (type 2) muscle fibers were studied in the gastrocnemius-soleus-Achilles unit of the rat. Both proteoglycans and glycosaminoglycans, type III collagen, fibronectin and laminin could be detected at the MTJ. Due to membrane folding, finger-like processes were seen at the myotendineal junction. The processes of the type 1 fibers are greater in size, however, due to subdivisions, the processes of type 2 muscle fibers had a greater surface than type 1 fibers. The macromolecular composition is similar in both type 1 and type 2 muscle fibers.