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Effects of impulse blockade on the contractile properties of rat skeletal muscle
Abstract:
1. Pressure was used to produce a localized block of impulse conduction in motor nerve fibres supplying rat plantaris and soleus muscles. After 1 week of inactivity both muscles exhibited marked atrophy of type I and type II muscle fibres. 2. In treated plantaris and soleus muscles the specific tetanic tensions were reduced to approximately half those of untreated control muscles; the specific twitch tensions were unchanged. The fall in specific tetanic tension in the nerve-blocked muscles was not associated with impaired excitation of muscle fibres during repetitive stimulation. 3. In nerve-blocked plantaris muscles the contraction and half-relaxation times became significantly prolonged whereas no change could be demonstrated in similarly treated soleus muscles. In both muscles the maximum rates of tetanic tension development increased following nerve block. 4. It is concluded that, in the rat, most of the changes in contractile properties and in muscle fibre size which follow denervation may be attributed to disuse rather than to interruption of axoplasmic transport.
Insights
Disuse, not nerve damage, causes most muscle atrophy and changes in contractile properties after denervation in rats. This study highlights the impact of inactivity on muscle fiber health.
Area of Science:
- Muscle physiology
- Neuroscience
- Skeletal muscle research
Background:
- Denervation leads to muscle atrophy and altered contractile properties.
- The roles of disuse and axoplasmic transport interruption in these changes are debated.
Purpose of the Study:
- To investigate the effects of localized nerve impulse conduction block on rat skeletal muscles.
- To differentiate the contributions of disuse versus axoplasmic transport interruption to post-denervation muscle changes.
Main Methods:
- Localized pressure-induced nerve block in rat plantaris and soleus muscles.
- Assessment of muscle fiber atrophy (Type I and II) after 1 week of inactivity.
- Measurement of specific tetanic and twitch tensions, contraction/relaxation times, and rates of tension development.
Main Results:
- Nerve block caused significant atrophy in both muscle fiber types.
- Specific tetanic tension halved, while specific twitch tension remained unchanged.
- Contraction and half-relaxation times prolonged in plantaris but not soleus; maximum tetanic tension development rates increased in both.
Conclusions:
- Disuse is the primary driver of muscle fiber atrophy and changes in contractile properties following denervation in rats.
- Interruption of axoplasmic transport plays a minimal role in these observed adaptations.