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Thin-filament length correlates with fiber type in human skeletal muscle.


ABSTRACT: Force production in skeletal muscle is proportional to the amount of overlap between the thin and thick filaments, which, in turn, depends on their lengths. Both thin- and thick-filament lengths are precisely regulated and uniform within a myofibril. While thick-filament lengths are essentially constant across muscles and species (?1.65 ?m), thin-filament lengths are highly variable both across species and across muscles of a single species. Here, we used a high-resolution immunofluorescence and image analysis technique (distributed deconvolution) to directly test the hypothesis that thin-filament lengths vary across human muscles. Using deltoid and pectoralis major muscle biopsies, we identified thin-filament lengths that ranged from 1.19 ± 0.08 to 1.37 ± 0.04 ?m, based on tropomodulin localization with respect to the Z-line. Tropomodulin localized from 0.28 to 0.47 ?m further from the Z-line than the NH(2)-terminus of nebulin in the various biopsies, indicating that human thin filaments have nebulin-free, pointed-end extensions that comprise up to 34% of total thin-filament length. Furthermore, thin-filament length was negatively correlated with the percentage of type 2X myosin heavy chain within the biopsy and shorter in type 2X myosin heavy chain-positive fibers, establishing the existence of a relationship between thin-filament lengths and fiber types in human muscle. Together, these data challenge the widely held assumption that human thin-filament lengths are constant. Our results also have broad relevance to musculoskeletal modeling, surgical reattachment of muscles, and orthopedic rehabilitation.

SUBMITTER: Gokhin DS 

PROVIDER: S-EPMC3287155 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Thin-filament length correlates with fiber type in human skeletal muscle.

Gokhin David S DS   Kim Nancy E NE   Lewis Sarah A SA   Hoenecke Heinz R HR   D'Lima Darryl D DD   Fowler Velia M VM  

American journal of physiology. Cell physiology 20111109 3


Force production in skeletal muscle is proportional to the amount of overlap between the thin and thick filaments, which, in turn, depends on their lengths. Both thin- and thick-filament lengths are precisely regulated and uniform within a myofibril. While thick-filament lengths are essentially constant across muscles and species (∼1.65 μm), thin-filament lengths are highly variable both across species and across muscles of a single species. Here, we used a high-resolution immunofluorescence and  ...[more]

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