Sarcomere-length dependence of myosin filament structure in skeletal muscle fibres of the frog

In this study, we investigated the effects of activation and stretch on the passive force–sarcomere length relationship in skeletal muscle. Single fibres from the lumbrical muscle of frogs were placed at varying sarcomere lengths on the descending limb of the force–sarcomere length relationship, and tetanic contractions, active stretches and passive stretches (amplitudes of ca 10% of fibre length at a speed of 40% fibre length/s) were performed. The passive forces following stretch of an activated fibre were higher than the forces measured after isometric contractions or after stretches of a passive fibre at the corresponding sarcomere length. This effect was more pronounced at increased sarcomere lengths, and the passive force–sarcomere length relationship following active stretch was shifted upwards on the force axis compared with the corresponding relationship obtained following isometric contractions or passive stretches. These results provide strong evidence for an increase in passive force that is mediated by a length-dependent combination of stretch and activation, while activation or stretch alone does not produce this effect. Based on these results and recently published findings of the effects of Ca 2+ on titin stiffness, we propose that the observed increase in passive force is caused by the molecular spring titin.

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Length dependence of force generation exhibit similarities between rat cardiac myocytes and skeletal muscle fibres

The Journal of Physiology ◽

10.1113/jphysiol.2010.190504 ◽

2010 ◽

Vol 588 (15) ◽

pp. 2891-2903 ◽

Cited By ~ 28

Author(s):

Laurin M. Hanft ◽

Kerry S. McDonald

Keyword(s):

Skeletal Muscle ◽

Cardiac Myocytes ◽

Force Generation ◽

Muscle Fibres ◽

Length Dependence ◽

Skeletal Muscle Fibres ◽

Rat Cardiac Myocytes

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Sarcomere length non-uniformity in relation to tetanic responses of stretched skeletal muscle fibres

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1978.0009 ◽

1978 ◽

Vol 200 (1138) ◽

pp. 109-116 ◽

Cited By ~ 20

Keyword(s):

Skeletal Muscle ◽

Thin Filament ◽

Sarcomere Length ◽

Muscle Fibres ◽

Plateau Region ◽

Constant Length ◽

Tension Response ◽

Force Velocity ◽

Skeletal Muscle Fibres ◽

Tetanic Tension

At sarcomere lengths above the plateau region of the length-tension diagram, it has been found that isometric tetanic tension is proportional to the amount of thick and thin filament overlap. This finding has been questioned recently and is reinvestigated here. Central segments of single frog skeletal muscle fibres were held at constant length during contractions at various sarcomere lengths above those associated with the plateau region. Tension records showed little or no creep, and the tetanic tensions measured at 0 and 20°C were inversely proportional to sarcomere length. These results extend and substantiate earlier findings. In contrast, when a stretched fibre had only its ends fixed during a tetanus, a different tension response was observed. The tension rise was initially very rapid but soon slowed to a gradual upward creep as stimulation was continued. This was followed by a tension decline. These tension phases were correlated with large decreases in sarcomere length at the fibre ends, while sarcomeres in the middle were extended a small amount. This tetanic tension response can be explained using the sarcomere length-tension relation and the force-velocity properties of muscle. These results strongly support the sliding filament, cross-bridge theory of muscle contraction.

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