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Developmental changes in crossbridge properties and myosin isoforms in hamster diaphragm
C Coirault1, F Lambert, T Joseph
1INSERM 451, Laboratoire d'Optique Appliquée, Ecole Polytechnique, Palaiseau, France.
American Journal of Respiratory and Critical Care Medicine
|October 6, 1997
Summary
Muscle maturation increases diaphragm force by adding more crossbridges, not by making them stronger. Myosin composition also shifts from slow to fast isoforms during development.
Area of Science:
- Muscle Physiology
- Developmental Biology
- Biochemistry
Background:
- Skeletal muscle undergoes significant functional and compositional changes during postnatal development.
- Understanding these changes is crucial for comprehending muscle maturation and its impact on respiratory function.
Purpose of the Study:
- To investigate the effects of maturation on crossbridge properties in hamster diaphragm muscle.
- To determine the changes in myosin isoform composition during postnatal development of the diaphragm.
Main Methods:
- Diaphragm muscle strips were collected from hamsters at different postnatal ages (Day 1, Day 8, and adulthood).
- Physiological measurements included peak isometric tension and maximum unloaded shortening velocity (Vmax).
- Crossbridge properties (single crossbridge force, number of crossbridges, myosin ATPase turnover rate, mechanical efficiency) were calculated using Huxley's equations.
- Myosin isoform composition was analyzed using electrophoresis.
Main Results:
- Peak isometric tension and Vmax increased significantly with age.
- The number of crossbridges (m) increased significantly from birth to adulthood, while single crossbridge force (pi) and mechanical efficiency (Effmax) remained unchanged.
- Myosin electrophoresis revealed a developmental shift from slow to fast myosin isoforms, with slow isoforms present at birth and fast isoforms increasing postnatally.
- Myosin ATPase turnover rate (kcat) increased significantly after the first week postpartum.
Conclusions:
- Diaphragm muscle force development is primarily attributed to an increase in the number of crossbridges, not alterations in individual crossbridge force or efficiency.
- The maturation of diaphragm muscle involves a significant shift in myosin isoform composition, correlating with changes in crossbridge kinetics.
- These developmental changes in crossbridge properties and myosin isoforms contribute to the enhanced force-generating capacity of the mature diaphragm.