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Effects of postnatal maturation on energetics and cross-bridge properties in rat diaphragm
Gilles Orliaguet1, Olivier Langeron, Belaid Bouhemad
1Department of Anesthesiology and Critical Care, Centre Hospitalo-Universitaire Necker-Enfants Malades, Assistance Publique-Hôpitaux de Paris, Université Paris V 75743 Paris Cedex 15, France. gorlia@club-internet.fr
Insights
Muscle cross-bridge (CB) properties mature significantly after the first week postpartum in rats. While single CB force remains constant, the total number of CBs increases, impacting muscle force and shortening velocity during development.
Area of Science:
- Muscle physiology
- Developmental biology
- Biophysics
Background:
- Understanding muscle maturation is crucial for pediatric and geriatric health.
- Cross-bridge (CB) dynamics are fundamental to muscle contraction.
- Postnatal diaphragm development involves significant physiological changes.
Purpose of the Study:
- To investigate the effects of postnatal maturation on rat diaphragm cross-bridge properties.
- To determine how muscle energetics and CB characteristics change with age.
- To compare diaphragm maturation across species.
Main Methods:
- Studied rat diaphragm strips at various postnatal ages (3, 10, 17 days, and adult).
- Calculated muscle energetics and CB characteristics using standard Huxley equations.
- Analyzed force-velocity relationships and mechanical efficiency.
Main Results:
- Maturation did not alter force-velocity relationship curvature or peak mechanical efficiency.
- A significant increase in CBs per cross-sectional area (m) was observed with aging, but not in single CB force.
- Myosin ATPase turnover increased, CB cycle duration decreased, and CB velocity decreased significantly after the first week postpartum.
- Linear relationships were found between maximum total force and m, and maximum unloaded shortening velocity and m.
Conclusions:
- Rat diaphragm maturation shows significant changes in CB number and cycling dynamics after the first week postpartum.
- Muscle force and shortening velocity are strongly correlated with the number of CBs per area.
- Postnatal diaphragm maturation appears to have limited species-specific differences between rats and hamsters.
Abstract:
The effects of maturation on cross-bridge (CB) properties were studied in rat diaphragm strips obtained at postnatal days 3, 10, and 17 and in adults (10-12 wk old). Calculations of muscle energetics and characteristics of CBs were determined from standard Huxley equations. Maturation did not change the curvature of the force-velocity relationship or the peak of mechanical efficiency. There was a significant increase in the total number of CBs per cross-sectional area (m) with aging but not in single CB force. The turnover rate of myosin ATPase increased, the duration of the CB cycle decreased, and the velocity of CBs decreased significantly only after the first week postpartum. There was a linear relationship between maximum total force and m (r = 0.969, P < 0.001), and between maximum unloaded shortening velocity and m (r = 0.728, P < 0.001). When this study in the rat and previous study in the hamster are compared, it appears that there are few species differences in the postnatal maturation process of the diaphragm.