Morphology and Histochemistry of the Myotendineal Junction of the Rat Calf Muscles

The macromolecular composition and morphometry of the myotendineal junction (MTJ) of slow-twitch (type 1) and fast-twitch (type 2) muscle fibers were studied in gastrocnemius-soleus-Achilles unit of the rat. Proteoglycans and glycosaminoglycans, type III collagen, fibronectin and laminin could be detected at the myotendineal junction. Due to the membrane folding finger-like processes were seen at the MTJ. The processes of type 1 fibers were greater in size. However, due to the subdivisions the processes of type 2 muscle fibers had a significantly greater surface length per muscle cell diameter than type 1 fibers. The myotendineal endings of both fiber types had a characteristic basal lamina, which was about three times thicker than in the longitudinal site of the same muscle cells. The basal lamina of type 1 fibers at the MTJ was significantly thicker than that of type 2 fibers.