title: Filamentous structures in skeletal muscle: anchors for the subsarcolemmal space.
abstract: In skeletal muscle fibers, intermediate filaments and actin filaments provide structural support to the myofibrils and the sarcolemma. For many years, it was poorly understood from ultrastructural observations that how these filamentous structures were kept anchored. The present study was conducted to determine the architecture of filamentous anchoring structures in the subsarcolemmal space and the intermyofibrils. The diaphragms (Dp) of adult wild type and mdx mice (mdx is a model for Duchenne muscular dystrophy) were subjected to tension applied perpendicular to the long axis of the muscle fibers, with or without treatment with 1% Triton X-100 or 0.03% saponin. These experiments were conducted to confirm the presence and integrity of the filamentous anchoring structures. Transmission electron microscopy revealed that these structures provide firm transverse connections between the sarcolemma and peripheral myofibrils. Most of the filamentous structures appeared to be inserted into subsarcolemmal densities, forming anchoring connections between the sarcolemma and peripheral myofibrils. In some cases, actin filaments were found to run longitudinally in the subsarcolemmal space to connect to the sarcolemma or in some cases to connect to the intermyofibrils as elongated thin filaments. These filamentous anchoring structures were less common in the mdx Dp. Our data suggest that the transverse and longitudinal filamentous structures form an anchoring system in the subsarcolemmal space and the intermyofibrils.
authors: Department of Anatomy, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma, 371-8511, Japan, astrid.khairani@gmail.com.
authors: Astrid Feinisa
authors: AF
authors: Khairani
authors: Yuki
authors: Y
authors: Tajika
authors: Maiko
authors: M
authors: Takahashi
authors: Hitoshi
authors: H
authors: Ueno
authors: Tohru
authors: T
authors: Murakami
authors: Arifin
authors: A
authors: Soenggono
authors: Hiroshi
authors: H
authors: Yorifuji
mesh_terms: D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000818:Animals; D003599:Cytoskeleton / Q000648:ultrastructure; D003964:Diaphragm / Q000648:ultrastructure; D007382:Intermediate Filaments / Q000648:ultrastructure*; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D046529:Microscopy, Electron, Transmission; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000648:ultrastructure*; D009210:Myofibrils / Q000648:ultrastructure; D012508:Sarcolemma / Q000648:ultrastructure*