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Protein turnover in skeletal muscle of suckling rats
T A Davis1, M L Fiorotto, H V Nguyen
1United States Department of Agriculture, Baylor College of Medicine, Houston, Texas 77030.
Insights
During rat suckling, skeletal muscle protein synthesis capacity declines while efficiency increases. This shift occurs earlier in weight-bearing muscles, correlating with developing mobility.
Area of Science:
- Physiology
- Molecular Biology
- Developmental Biology
Background:
- Skeletal muscle growth and development are critical during the suckling period.
- Understanding protein turnover dynamics is essential for comprehending muscle mass accretion.
Purpose of the Study:
- To investigate in vivo changes in skeletal muscle protein synthesis during rat suckling (1-28 days).
- To differentiate protein synthetic capacity and efficiency variations among different muscle types.
Main Methods:
- Utilized a flooding dose of L-[4-3H]phenylalanine to measure protein synthesis in rat soleus, plantaris, anterior tibialis, and extensor digitorum longus (EDL) muscles.
- Quantified protein mass and RNA content to assess protein synthetic capacity and efficiency.
Main Results:
- Skeletal muscle mass and RNA content increased significantly (100-fold and 20-fold, respectively) from day 1 to 28.
- Fractional protein synthesis rates (Ks) decreased, driven by reduced protein synthetic capacity (RNA/protein ratio).
- Protein synthetic efficiency (protein synthesized/RNA) increased, with earlier gains observed in weight-bearing muscles (soleus, plantaris) compared to non-weight-bearing muscles (anterior tibialis, EDL).
Conclusions:
- Skeletal muscle protein synthetic capacity diminishes during rat suckling, while efficiency enhances.
- Increased translational efficiency in weight-bearing muscles precedes that in non-weight-bearing muscles, linked to the onset of mobility.
Abstract:
To determine the normal changes in protein turnover of skeletal muscle in vivo during the suckling period of rats, protein synthesis was measured in soleus, plantaris, anterior tibialis, and extensor digitorum longus (EDL) muscles of 1- to 28-day-old rats using a flooding dose of L-[4-3H]phenylalanine. Protein mass of hind-limb muscles increased nearly 100-fold, and RNA increased approximately 20-fold between 1 and 28 days of age. The total amount of protein synthesized per day increased 34-fold. Fractional protein synthesis rates (Ks) decreased two- to threefold between 1 and 28 days postpartum as a result of a decrease in protein synthetic capacity (RNA/protein). Protein synthetic efficiency (total protein synthesized/RNA) increased during this period. Ks were similar among the four muscles at 1-10 days. At 16 days, Ks increased in soleus and plantaris as a result of increases in protein synthetic efficiency; Ks did not increase in anterior tibialis and EDL. These data suggest that, during the suckling period, protein synthetic capacity in skeletal muscles of rats declines, while protein synthetic efficiency increases. The increase in translational efficiency occurred earlier in weight-bearing muscles (soleus, plantaris) than in non-weight-bearing muscles (anterior tibialis and EDL) and was associated with the appearance of mobility.