Sarcomere Length Changes in Single Frog Muscle Fibres during Tetani at Long Sarcomere Lengths
Laser diffraction and photomicrography have been used to monitor sarcomere length changes in single muscle fibres of the frog, at long sarcomere lengths, during fixed end tetani.
In the central 90% of all fibres, changes in sarcomere length were consistently less than 0.25 μm. Sarcomere length showed an initial rapid change, followed by a progressively slower increase, which persisted throughout a 4s tetanus. Sarcomere length in the terminal 200–400 μm segment at each end of a fibre decreased rapidly by up to 1 μm in the first second of a tetanus. This shortening was accompanied by a marked increase in disorder of the striation pattern.
Maximum isometric tensions in fixed end tetani were much greater than those predicted by crossbridge theory over the entire range of sarcomere lengths studied. An analysis of the intersarcomere dynamics suggests that this extra tension may be explained by known phenomena on the basis of a progressive increase in sarcomere length dispersion along the fibre.
KeywordsSarcomere Length Isometric Tension Single Muscle Fibre Frog Skeletal Muscle Tension Record
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