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Evidence for increased myofibrillar mobility in desmin-null mouse skeletal muscle

Sameer B. Shah¹, Fong-Chin Su², Kimberly Jordan¹, Derek J. Milner³, Jan Fridén⁴, Yassemi Capetanaki³ and Richard L. Lieber^1,*

¹ Departments of Orthopaedics and Bioengineering, Veterans Affairs Medical Center and University of California at San Diego, San Diego, CA 92093, USA,
² Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan,
³ Department of Cell Biology, Baylor College of Medicine, Houston, TX 77030, USA and
⁴ Department of Hand Surgery, Sahlgrenska University Hospital, Göteborg, Sweden

View larger version (113K): [in a new window]   Fig. 1. Electron micrographs of the extensor digitorum longus fifth toe muscle from wild-type (A) or desmin-null (B) animals fixed under conditions of passive loading, displaying the method for digitizing Z-disk endpoints to yield horizontal Z-disk displacement (xmyo) and sarcomere length (SL). Note the greater stagger in adjacent Z disks in muscle from knockout versus wild-type animals. For the frames displayed (approximately one-fifteenth the area of a full micrograph), for (A), xmyo=0.09 µm and SL=3.57 µm, for (B), xmyo=0.58 µm and SL=3.60 µm. The calibration is identical for both micrographs. Scale bar, 1 µm.

View larger version (13K): [in a new window]   Fig. 2. Horizontal Z-disk displacement (xmyo) plotted versus sarcomere length (SL) for extensor digitorum longus fifth toe muscles of wild-type (circles) and desmin-null (squares) animals. Superficial regions are shown with open symbols while deep regions are shown with filled symbols. Note that xmyo increases to a greater extent as SL increases in muscles from knockout compared with wild-type animals. Error bars represent ±1 S.E.M. in either the xmyo or SL direction (N=7 wild-type muscles and N=9 desmin-null muscles). Superficial and deep regions of each muscle were sampled from 10 micrographs per region. The regression slope of the xmyo versus SL relationship was significantly different from zero in the specimens from knockout animals (P<0.005) but not in the specimens from wild-type animals (P>0.4), and analysis of covariance (ANCOVA) revealed a significant difference between the slopes of these relationships (P<0.05).