Three-Dimensional Structure of the Z Band in a Normal Mammalian Skeletal Muscle

• Published in: The Journal of cell biology 1996-05, Vol.133 (3), p.571-583
• Main Authors: Schroeter, John P., Bretaudiere, Jean-Pierre, Sass, Ronald L., Goldstein, Margaret A.
• Format: Article
• Language: English
• Subjects: Actins; Animals; Cellular biology; Cross-Linking Reagents - chemistry; Crystal lattices; Electron micrographs; Electron microscopy; Histograms; Image Processing, Computer-Assisted; Mammals; Microscopy, Electron; Muscle Contraction - physiology; Muscle Proteins - chemistry; Muscle, Skeletal - chemistry; Muscle, Skeletal - ultrastructure; Muscles; Muscular system; Rats; Rats, Sprague-Dawley; Sarcomeres; Sarcomeres - chemistry; Sarcomeres - ultrastructure; Skeletal muscle; Skeletal system; Vertebrates; Wave diffraction
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.133.3.571

The three-dimensional structure of the vertebrate skeletal muscle Z band reflects its function as the muscle component essential for tension transmission between successive sarcomeres. We have investigated this structure as well as that of the nearby I band in a normal, unstimulated mammalian skeletal muscle by tomographic three-dimensional reconstruction from electron micrograph tilt series of sectioned tissue. The three-dimensional Z band structure consists of interdigitating axial filaments from opposite sarcomeres connected every 18 ± 12 nm (mean ± SD) to one to four cross-connecting Z-filaments. Most often, the cross-connecting Z-filaments are observed to meet the axial filaments in a fourfold symmetric arrangement. The substantial variation in the spacing between cross-connecting Z-filament to axial filament connection points suggests that the structure of the Z band is not determined solely by the arrangement of α-actinin to actin-binding sites along the axial filament. The cross-connecting filaments bind to or form a "relaxed interconnecting body" halfway between the axial filaments. This filamentous body is parallel to the Z band axial filaments and is observed to play an essential role in generating the small square lattice pattern seen in electron micrographs of unstimulated muscle cross sections. This structure is absent in cross sections of the Z band from muscles fixed in rigor or in tetanus, suggesting that the Z band lattice must undergo dynamic rearrangement concomitant with crossbridge binding in the A band.