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Spring‑like vibrations in muscle: solving the mystery hidden in their ‘dents’
Spring‑like vibrations in muscle: solving the mystery hidden in their ‘dents’
Striated muscles—heart and skeletal muscle—are built from serially aligned sarcomeres. Their repeated contraction and relaxation produce macroscopic muscle force and cardiac rhythm. In this study we simultaneously analyzed both (i) sarcomeric oscillation (changes in individual sarcomere length) and (ii) Z‑line oscillation (the boundary motion between sarcomeres, here called sarcosynced oscillation) using two physical indices, instantaneous amplitude and instantaneous phase. The method provides a fine‑grained view of the “wave” dynamics generated along the myofibril.
When skeletal‑muscle fibers were driven at constant calcium concentration, two unexpected findings emerged:
Defect holes during one‑way propagation – As a contraction wave travels, a transient collapse—a local dent—appears in both sarcomere length and Z‑line motion.
Collision holes at wave–wave impacts – Where two waves meet, a persistent defect develops.
The sharp drop in instantaneous amplitude of the Z‑line oscillation, accompanied by a sudden phase jump, marks these defects. We term the transient defect a Sarcomeric‑Defect Hole (SD hole) and the collision‑induced one a Sarcomeric‑Collision Hole (SC hole) and perform a detailed quantitative analysis.
A: Time series of Z‑line oscillations (sarcosynced oscillations) from 31 consecutive Z‑lines.
B: Time series of inter‑Z‑line distance for 30 sarcomeres (sarcomeric oscillations).
C/D: Spatiotemporal maps of instantaneous amplitude for Z‑line and sarcomere oscillations, respectively.
E/F: Corresponding maps of instantaneous phase.
G/H: Close‑up at 4 s: an SD hole in the Z‑line trace—abrupt amplitude loss and phase jump. Concurrent sarcomeric oscillation behavior at the same cross‑section.
Significance
Significance
These hole phenomena represent the scars left when a propagating contraction wave breaks down or when two waves collide. They provide an objective handle on collective sarcomere dynamics—coherence, mismatch, and re‑synchronization. Notably, because the Z‑line signal alone suffices to infer sarcomere‑wave state, this approach could underpin non‑invasive evaluation of the mechanical properties of heart and skeletal muscle.
By quantifying muscle waves through instantaneous amplitude/phase and exposing abnormalities as holes, this work offers a cutting‑edge analytical framework with potential impact on muscle disease diagnostics, regenerative medicine, and biomechanics.
Article information & citation
Seine A. Shintani. Hole behavior captured by analysis of instantaneous amplitude and phase of sarcosynced oscillations reveals wave characteristics of sarcomeric oscillations. Biochemical and Biophysical Research Communications, 691: 149339, 2024.
https://doi.org/10.1016/j.bbrc.2023.149339
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