Intermediate filaments connect Z-discs in adult chicken muscle

When adult chicken skeletal myofibrils are treated with a myosin‐extracting solution, the Z‐discs with attached actin filaments retain their linear connections with one another in the extracted myofibril. The sarcomere length increases in the extracted myofibrils from a control length of 2.5 μm up to 6 μm. In a sarcomer, eight to fifty 10 nm filaments can be seen in parallel array in the H‐zone. The 10nm‐wide filaments do not bind heavy meromyosin and are two to four μm in length. These intermediate filaments are postulated to be an integral part of the sarcomere, connecting Z‐bands along the length of the myofibril.