Browsing by Author "Li, Meng"

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    Gaining New Understanding of Sarcomere Length Nonuniformities in Skeletal Muscles
    (2023-09-28) Li, Meng; Herzog, Walter; Syme, Douglas; Joumaa, Venus
    Sarcomere lengths are non-uniform on all structural levels of mammalian skeletal muscle. These non-uniformities have been associated with a variety of mechanical properties, including residual force enhancement and depression, creep, increased force capacity, and extension of the plateau of the force-length relationship. However, the nature of sarcomere length non-uniformities has not been explored systematically. The purpose of this study was to determine the properties of sarcomere length non-uniformities in active and passive muscle. Single myofibrils of rabbit psoas (n=20; with 412 individual sarcomeres) were subjected to three activation/deactivation cycles at short, intermediate, and long sarcomere lengths of 2.7, 3.2, and 3.6 µm respectively, and individual sarcomere lengths were measured at 4 passive and 3 active points during the activation/deactivation cycles. The primary results were that sarcomere length non-uniformities did not occur randomly but were governed by some structural and/or contractile properties of the sarcomeres and that sarcomere length non-uniformities differed greatly between the active and passive state. We propose that the mechanisms that govern the systematic sarcomere lengths non-uniformities observed in active and passive muscle are associated with the variable number of contractile proteins and the variable number and stiffness of titin filaments in individual sarcomeres.