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Inhibition of denervation changes in skeletal muscle by blockers of protein synthesis
Abstract:
1. A study was made of the effects of inhibitors of protein synthesis (actinomycin D, chloramphenicol and cycloheximide) on the in vivo development of extrajunctional cholinergic receptors, tetrodotoxin-resistant action potentials, slowing of the time course of the action potential, and on the fall in the resting membrane potential in denervated mouse skeletal muscle.2. Actinomycin D (0.5 mg/kg, I.P.) reduced the incorporation of uridine into skeletal muscle by 50-60% for 4-5 days. There was no simultaneous reduction in L-leucine incorporation.3. Actinomycin D (0.5 mg/kg I.P., 1 day after denervation) inhibited the development of extrajunctional cholinergic receptors, tetrodotoxin-resistant action potentials and the fall in resting membrane potential for approximately 4 days.4. The post-denervation fall in the maximum rate of rise and in the amplitude of the overshoot of the muscle fibre action potential was unaffected by actinomycin D treatment.5. Actinomycin D failed to inhibit the appearance of the membrane changes if given later than 2 days after denervation.6. Chloramphenicol (6 g/kg in divided doses) and cycloheximide (40 g/kg every 12 hr) were also able to inhibit the appearance of the membrane changes.7. It is concluded that some denervation induced changes in the muscle fibre membrane depend on the synthesis of new proteins. The results imply that the motor nerve cell normally exerts a regulatory influence on the genome of the muscle cell.
Insights
Protein synthesis inhibitors like actinomycin D block the development of new muscle membrane properties after denervation. These findings suggest nerve cells regulate muscle cell gene expression.
Area of Science:
- Neuroscience
- Molecular Biology
- Muscle Physiology
Background:
- Denervation of skeletal muscle triggers significant changes in the muscle fiber membrane.
- These changes include the development of extrajunctional cholinergic receptors and altered action potential properties.
Purpose of the Study:
- To investigate the role of protein synthesis in the in vivo development of denervation-induced membrane changes in mouse skeletal muscle.
- To determine if inhibiting protein synthesis affects the formation of extrajunctional receptors and action potential alterations post-denervation.
Main Methods:
- Administration of protein synthesis inhibitors (actinomycin D, chloramphenicol, cycloheximide) to denervated mice.
- Measurement of uridine and L-leucine incorporation into skeletal muscle.
- Electrophysiological assessment of muscle fiber action potentials and resting membrane potential.
Main Results:
- Actinomycin D significantly inhibited the development of extrajunctional cholinergic receptors, tetrodotoxin-resistant action potentials, and resting membrane potential fall for up to 4 days.
- Inhibition of protein synthesis by chloramphenicol and cycloheximide also prevented these denervation-induced membrane changes.
- Actinomycin D was ineffective if administered more than 2 days after denervation.
- The rate of rise and amplitude of the action potential overshoot were not affected by actinomycin D.
Conclusions:
- Denervation-induced alterations in the muscle fiber membrane are dependent on the synthesis of new proteins.
- These results indicate that motor neurons exert a regulatory influence on the muscle cell's genome.
- The findings highlight the dynamic interplay between nerve and muscle at the molecular level.