Macromolecular composition of the myotendinous junction.

The macromolecular composition of the myotendinous junction of the rat Achilles tendon was investigated. Heparan sulphate, chondroitin sulphate, and/or dermatan sulphate could be detected in the terminal processes of the muscle cells, but neither heparin nor keratan sulphate was present. The presence of hyaluronic acid was also questionable. High concentrations of sulphate containing glycosaminoglycans could be demonstrated both in the sarcolemma membranes and extracellular region. The main collagenous component in the myotendinous junction was type I collagen. Also small amounts of type III collagen was found at the myotendinous interface. In addition, high concentrations of fibronectin was present on the muscle cell surfaces of the junction. These results showed that myotendinous junction is histochemically and immunohistochemically a highly specified area rich in various polysaccharides. The high concentration of the polysaccharides in the myotendinous interface may increase the adhesive force between the muscle cell membrane and tendineal collagen fibrils and, by this way, it may be important in improving the elastic buffer capacity of the junction against loading.