Ultrastructural study of the muscle cell surface.

In human muscle fibers and using tannic acid-glutaraldehyde fixation and freeze-fracture deepetch rotary replication, trabecular structures connecting the basal lamina to the outer leaflet of the muscle plasma membrane were observed. The trabeculae were noted at all levels of the sarcomere in regions away from the myotendinous junction. It is suggested that trabecular structures connecting the basal lamina to the plasma membrane may be a universal feature of the muscle cell surface.