Transverse bands in smooth muscle cells.

In several preparations of intestinal musculature of mammals and other vertebrates, the smooth muscle cells showed distinct transverse striations. Their distribution was irregular, but they were often in register in adjacent cells. They were studied by light and electron microscopy, and it was concluded that they represent areas where the muscle cells had been crumpled, probably during or after fixation, especially in muscles that are curved and arranged in concentric arrays. A characteristic disruption in the arrangement of myofilaments was observed. These striations were not seen in control preparations of the guinea-pig taenia coli; however, when the taenia was wound around a rod after partial or complete fixation, transverse striations became apparent in the concave part of the coiled-up strip of muscle. The longitudinal compression of the muscle cells, which were made somewhat rigid by the fixation, is the most likely explanation of the transverse bands.