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Contractile properties of the rat external abdominal oblique and diaphragm muscles during development
J F Watchko1, B S Brozanski, T L O'Day
1Department of Pediatrics, Magee-Womens Hospital, University of Pittsburgh School of Medicine, Pennsylvania 15213.
Insights
Postnatal development alters rat external abdominal oblique (EAO) and costal diaphragm (DIA) muscle properties. Contractile and fatigue characteristics diverge with age, suggesting distinct roles in ventilation.
Area of Science:
- Physiology
- Developmental Biology
- Muscle Physiology
Background:
- The external abdominal oblique (EAO) and costal diaphragm (DIA) muscles are crucial for ventilation.
- Understanding their developmental changes is key to comprehending respiratory mechanics.
Purpose of the Study:
- To investigate the in vitro contractile and fatigue properties of rat EAO and DIA muscles during postnatal development.
- To compare the developmental trajectories of these two key respiratory muscles.
Main Methods:
- Isometric twitch contraction and half-relaxation times were measured.
- Force-frequency relationships were analyzed.
- Muscle fatigability was assessed.
Main Results:
- Both EAO and DIA muscles showed age-related decreases in contraction and relaxation times.
- Early postnatal development saw longer contractile times in EAO compared to DIA, reversing in adults.
- Specific force increased with age in both muscles, while fatigability increased with development, with adult EAO being more fatigable than DIA.
Conclusions:
- EAO and DIA muscles exhibit distinct postnatal developmental transitions in contractile and fatigue properties.
- These differing developmental patterns may correlate with their specific functional roles in maintaining ventilation throughout life.
Abstract:
We studied the in vitro contractile and fatigue properties of the rat external abdominal oblique (EAO) and costal diaphragm (DIA) muscles during postnatal development. Isometric twitch contraction (CT) and half-relaxation (RT1/2) times were longer in both the EAO and DIA muscles during the early postnatal period and decreased with age. In the first postnatal week, the CT and RT1/2 were longer in the EAO than the DIA muscle. At 14 days of age and thereafter, the CT and RT1/2 were shorter in the EAO than in the DIA muscle. Force-frequency relationships of the EAO and DIA muscles changed during postnatal development such that the relative force (percent maximum) generated at lower frequencies (less than 15 pulses/s) decreased with age. Moreover the relative force generated by the EAO muscle at lower frequencies was greater than that of the DIA muscle during the early postnatal period but less than that of the DIA muscle in adults. The specific force of both the EAO and DIA muscles increased progressively with age. There were no differences in specific force between the EAO and DIA muscles at any age. The fatigability of the EAO and DIA muscles was comparable during the early postnatal period and increased in both muscles with postnatal development. In adults the EAO muscle was more fatigable than the DIA muscle. We conclude that the contractile and fatigue properties of the EAO and DIA muscles undergo significantly different postnatal transitions, which may reflect their functional involvement in sustaining ventilation.