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Respiratory muscle fatigue resistance relates to myosin phenotype and SDH activity during development
1Department of Pediatrics, Magee-Womens Hospital, University of Pittsburgh School of Medicine, Pennsylvania 15213.
Insights
Muscle fatigue resistance in developing rats is strongly linked to myosin heavy chain (MHC) expression, not oxidative capacity alone. MHC phenotype significantly predicts fatigue resistance in respiratory muscles.
Area of Science:
- Physiology
- Developmental Biology
- Muscle Biology
Background:
- Muscle fatigue resistance (FR) is crucial for respiratory and postural functions.
- Understanding developmental changes in muscle FR is key to pediatric and exercise physiology.
- Myosin heavy chain (MHC) isoforms and oxidative capacity influence muscle performance.
Purpose of the Study:
- To correlate fatigue resistance (FR) of rat diaphragm (DIA) and external abdominal oblique (EAO) muscles during postnatal development.
- To investigate the relationship between FR, MHC phenotypes, and oxidative capacities (succinic dehydrogenase activity).
Main Methods:
- In vitro isometric contractions using the Burke fatigue test to measure FR.
- Quantitative measurement of succinic dehydrogenase (SDH) enzyme activity for oxidative capacity.
- Analysis of MHC isoform content to determine MHC phenotype.
Main Results:
- FR was high in newborns and decreased with development in both DIA and EAO.
- SDH activity was low in neonates, increased, then declined to adult levels.
- FR correlated significantly with MHC phenotype (r2 = 0.88) but not SDH activity (r2 = 0.01).
- MHC phenotype explained 60% of developmental variance in FR.
- Combining SDH and MHC phenotype improved correlation (r2 = 0.99).
Conclusions:
- Developmental changes in respiratory muscle FR are primarily driven by MHC phenotype.
- A balance between MHC isoform composition and oxidative capacity influences FR.
- MHC phenotype is a strong predictor of muscle fatigue resistance during development.
Abstract:
We correlated the fatigue resistance (FR) of the costal diaphragm (DIA) and external abdominal oblique (EAO) of the rat during postnatal development with their respective 1) myosin heavy chain (MHC) phenotypes and 2) oxidative capacities [indexed by quantitative measurements of succinic dehydrogenase (SDH) enzyme activity]. FR was measured in vitro during isometric contractions with the use of the Burke fatigue test. FR of the DIA and EAO was high in newborns and declined during postnatal development. SDH activity was uniformly low in neonatal DIA and EAO and increased during early postnatal development before declining to adult levels. FR did not significantly correlate with SDH activity (r2 = 0.01) but did relate to the MHC phenotype as indexed by the ratio of adult MHC isoform content (slow + IIa + IIx + IIb) to developmental MHC isoform content (slow + neonatal; r2 = 0.88, P < 0.01). Stepwise regression revealed that neonatal MHC expression alone accounted for 60% of the developmental variance in FR. The correlation between FR and MHC phenotype was improved if SDH was also considered, i.e., the ratio of SDH to MHC phenotype (r2 = 0.99, P < 0.01). We conclude that FR of respiratory muscle during development relates to a balance between the energetic demands of the muscle contractile proteins as reflected by MHC isoform composition and its oxidative capacity with MHC phenotype alone exerting a strong predictive effect on FR.