Surface cables of vertebrate muscle cells

Cardiac and skeletal muscle cells were examined by scanning electron microscopy (SEM) for the presence of cell surface cables. This is the first report of such structures in the non-mammalian species, the pigeon, and in skeletal muscle of any species. They previously been reported from hamster cardiac myocytes. Cables were demonstrated on skeletal and heart muscle cells of both pigeons and hamsters. However, they could be visualized in skeletal muscle and pigeon heart only at short sarcomere lengths induced by homogenizing the tissues with additional CaCl2. Cables in the various preparations varied in length between 160 +/- 93 nm (mean +/- S. D.) and 220 +/- 54 nm. Heart cables has a mean diameter of 60 nm and skeletal muscle cables a mean diameter of 50 nm, as measured in metal-coated SEM preparations prepared simultaneously. This difference was significant (p less than 0.02) in hamsters and and highly significant (p less than 0.001) in pigeons. Cables reached the greatest concentration in hamster heart prepared with added CaCl2 (9.1 +/- 2.4 cables per linear transverse micrometer). The function of the cables, and their chemical nature, are not known. They may represent the anatomic basis for the limited compliance of heart muscle at long sarcomere lengths, and/or they may be a component of the intercellular fibrillar network of the heart.