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Updated: Aug 14, 2026
Isolating Myofibrils from Skeletal Muscle Biopsies and Determining Contractile Function with a Nano-Newton Resolution Force Transducer
Published on: May 7, 2020
Studies on the post-mortem fragmentation of myofibrils
Abstract:
1. There was a close relationship between the fragmentation of myofibrils and the tension developed during post-mortem contraction of muscle. The extent of fragmentation was at its maximum when the sarcomeres attained a length of 2.0 to 2.2 micron. 2. The rate of fragmentation of myofibrils depended upon the calcium ion concentration within a range of 10(-5) to 2 x 10(-2) M, with a minimum at pH 6.5. The fragmentation of myofibrils free from muscle fibers was not affected by 10 mM iodoacetate, an irreversible inhibitor of calcium-activated factor (CAF). 3. Incubation of myofibrils with 10 mM CaCl2 caused the release of about 12% of the total myofibrillar proteins after homogenization. The protein solution contained little alpha-actinin, and considerable amounts of 54,000- and 76,000-dalton components which seem to originate from the Z-line. SDS-polyacrylamide gels of troponin prepared from the incubated myofibrils did not change with time of incubation. These findings are in contrast with the proteolytic degradation of Z-lines by CAF treatment, in which alpha-actinin and 87,000 dalton component are released. 4. These data directly demonstrate that the in vitro fragmentation of post-mortem muscle (i.e. duirng its conversion into myofibrils upon mechanical homogenization) is different from that induced by CAF. The possible role of calcium ions during in vitro fragmentation of myofibrils is discussed.
Insights
Post-mortem muscle contraction involves myofibril fragmentation, influenced by calcium ion concentration and sarcomere length. This in vitro fragmentation differs from calcium-activated factor-induced degradation.
Area of Science:
- Muscle physiology
- Biochemistry
- Post-mortem meat science
Background:
- Muscle contraction and relaxation are complex processes involving myofibril structure.
- Understanding post-mortem muscle changes is crucial for meat quality.
- Calcium ions play a significant role in muscle function and degradation.
Purpose of the Study:
- To investigate the relationship between myofibril fragmentation and tension during post-mortem muscle contraction.
- To determine the influence of calcium ion concentration and pH on myofibril fragmentation rate.
- To differentiate in vitro myofibril fragmentation from calcium-activated factor (CAF) induced degradation.
Main Methods:
- Measurement of myofibril fragmentation extent and sarcomere length during post-mortem contraction.
- Analysis of myofibril fragmentation rate across varying calcium ion concentrations and pH.
- Incubation of myofibrils with calcium chloride and assessment of protein release using SDS-polyacrylamide gel electrophoresis.
- Comparison of fragmentation patterns with CAF treatment.
Main Results:
- Myofibril fragmentation closely correlated with tension development, peaking at sarcomere lengths of 2.0-2.2 µm.
- Fragmentation rate was dependent on calcium ion concentration (10⁻⁵ to 2x10⁻² M) with a minimum at pH 6.5.
- In vitro fragmentation released specific Z-line components (54,000 and 76,000 daltons) and minimal alpha-actinin, distinct from CAF effects.
- Iodoacetate did not inhibit fragmentation of isolated myofibrils, suggesting a non-CAF mechanism.
Conclusions:
- In vitro myofibril fragmentation during mechanical homogenization is mechanistically distinct from CAF-induced proteolysis.
- Calcium ions play a role in the in vitro fragmentation of post-mortem muscle myofibrils.
- The identified protein fragments suggest specific Z-line involvement in calcium-mediated in vitro fragmentation.
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