Isotonic force modulates force redevelopment rate of intact frog muscle fibres: Evidence for cross-bridge induced thin filament activation

Rene Vandenboom, James D. Hannon, Gary C Sieck

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Abstract

We tested the hypothesis that force-velocity history modulates thin filament activation, as assessed by the rate of force redevelopment after shortening (+dF/dtR). The influence of isotonic force on +dF/dtR was assessed by imposing uniform amplitude (2.55 to 2.15 μm sarcomere-1) but different speed releases to intact frog muscle fibres during fused tetani. Each release consisted of a contiguous ramp- and step-change in length. Ramp speed was changed from release to release to vary fibre shortening speed from 1.00 (2.76 ± 0.11 μm half-sarcomere-1 s-1) to 0.30 of maximum unloaded shortening velocity (Vu), thereby modulating isotonic force from 0 to 0.34 Fo, respectively. The step zeroed force and allowed the fibre to shorten unloaded for a brief period of time prior to force redevelopment. Although peak force redevelopment after different releases was similar, +dF/dtR increased by 81 ± 6% (P < 0.05) as fibre shortening speed was reduced from 1.00 Vu. The +dF/dtR after different releases was strongly correlated with the preceding isotonic force (r = 0.99, P < 0.001). Results from additional experiments showed that the slope of slack test plots produced by systematically increasing the step size that followed each ramp were similar. Thus, isotonic force did not influence Vu (mean: 2.84 ± 0.10 μm half-sarcomere-1 s-1, P < 0.05). We conclude that isotonic force modulates +dF/dtR independent of change in Vu, an outcome consistent with a cooperative influence of attached cross-bridges on thin filament activation that increases cross-bridge attachment rate without alteration to cross-bridge detachment rate.

Original languageEnglish (US)
Pages (from-to)555-566
Number of pages12
JournalJournal of Physiology
Volume543
Issue number2
DOIs
StatePublished - Sep 1 2002

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Sarcomeres
Architectural Accessibility
Anura
Muscles
Tetanus
History

ASJC Scopus subject areas

  • Physiology

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Isotonic force modulates force redevelopment rate of intact frog muscle fibres : Evidence for cross-bridge induced thin filament activation. / Vandenboom, Rene; Hannon, James D.; Sieck, Gary C.

In: Journal of Physiology, Vol. 543, No. 2, 01.09.2002, p. 555-566.

Research output: Contribution to journalArticle

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