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October 1, 1969Proceedings of the National Academy of SciencesOpen Access

Cross-Bridge Properties Derived From Muscle Isotonic Velocity Transients

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Key result

The turnover of cross-bridges for a given contraction distance is independent of the speed of the motion, with a cross-bridge formed each time an actin site comes within range of a myosin projection.

Population

Frog muscle fiber preparations and a digital computer simulation model of cross-bridge turnover

Comparison

Step decreases in load vs Isometric contraction and varying force steps

Design

Preclinical

Authors

RPRichard J. PodolskyNational Institutes of HealthANA. C. NolanUniversity of ChicagoSZS. A. ZavelerNational Institutes of Health

Discussion

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Implication

Supports quantitative cross-bridge models; leaves open direct applicability to human cardiac sarcomere function.

Key Points

  • This research aims to determine the rate constants for cross-bridge turnover during frog muscle contraction.
  • Analyzed motion following step decreases in load during muscle contraction.
  • Examined the range of attachment for myosin projections on actin filaments.
  • Measured displacement of attachment sites during contraction.
  • Determined that myosin projections can attach to actin filaments within a range of about 100 A.
  • Indicated that turnover of cross-bridges occurs independently of the motion speed.
  • Found that each time an actin site is in range, a cross-bridge is formed.

Structured PICO

P
Population
Frog muscle fiber preparations and a digital computer simulation model of cross-bridge turnover
I
Intervention
Step decreases in load (isotonic velocity transients)
C
Comparator
Isometric contraction and varying force steps
O
Outcome
Rate constants for the turnover of cross-bridges (f and g) and cross-bridge compliancesurrogate

The study demonstrates that cross-bridge turnover for a given contraction distance is independent of contraction speed, with an interaction range of approximately 100 Å.

Limitations

  • The magnitude of the displacement deviation in the model is about half of that seen in the actual motion
  • Second null times for larger force steps are not seen in the model motion
  • Magnitude of the displacement deviation in the model is about half of that seen in the actual motion
  • Second null times for the larger force steps are not seen in the model motion

Cite This Study

Podolsky et al. (1969) studied Frog muscle contraction. Step decreases in load was evaluated on Rate constants for the turnover of cross-bridges. The turnover of cross-bridges for a given contraction distance is independent of the speed of the motion, with a cross-bridge formed each time an actin site comes within range of a myosin projection.

synapsesocial.com/papers/6a6ba5fa47a1bfb288f3385ahttps://doi.org/10.1073/pnas.64.2.504
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Also Consider

Synapse has enriched 3 closely related papers on similar clinical questions. Consider them for comparative context:

  1. 1THE DOUBLE ARRAY OF FILAMENTS IN CROSS-STRIATED MUSCLE1957 · 645 citations
  2. 2Tension development in highly stretched vertebrate muscle fibres1966 · 349 citations
  3. 3The effect of load on the heat of shortening of muscle1964 · 260 citations