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X-ray diffraction studies on muscle during rapid shortening and their implications concerning crossbridge behaviour
H E Huxley1, M Kress, A F Faruqi
1MRC Laboratory of Molecular Biology, Cambridge, U.K.
Advances in Experimental Medicine and Biology
|January 1, 1988
Summary
Muscle crossbridge detachment increases during shortening, detectable via X-ray diffraction. This finding suggests a significant population of detached crossbridges exists during muscle contraction.
Area of Science:
- Muscle physiology
- Biophysics
- Structural biology
Background:
- Muscle contraction involves myosin crossbridges cycling between attached and detached states.
- During isometric contraction, crossbridges remain largely attached and cycling is slow.
- Understanding crossbridge dynamics during shortening is crucial for muscle function.
Purpose of the Study:
- To investigate the existence and dynamics of detached crossbridges during muscle shortening.
- To determine if a significant population of detached crossbridges can be detected.
- To correlate X-ray diffraction patterns with crossbridge states during contraction.
Main Methods:
- Utilizing equatorial X-ray diffraction patterns to observe muscle structure during contraction.
- Analyzing the intensity changes of actin layer line reflections (59 A and 51 A).
- Comparing diffraction patterns during isometric contraction versus high-speed shortening.
Main Results:
- X-ray diffraction indicates a significant population of detached crossbridges at higher shortening speeds.
- The detachment rate can reach approximately 200 per second during rapid shortening.
- Decreased intensity of 59 A and 51 A actin layer lines suggests changes in attached crossbridge populations, not actin complex structure.
Conclusions:
- Evidence supports the presence of a substantial detached crossbridge population during muscle shortening.
- Changes in actin layer line intensities are likely due to altered numbers of attached or tension-generating crossbridges.
- Findings support helical labeling of actin structure by crossbridges during muscle contraction.
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