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Decrease in resting calcium and calcium entry associated with slow-to-fast transition in unloaded rat soleus muscle.
Bodvaël Fraysse1, Jean-François Desaphy, Sabata Pierno
1Sezione di Farmacologia, Dipartimento Farmaco-Biologico, Università degli Studi di Bari, Via Orabona 4-Campus, 70125, Bari, Italy.
Summary
Muscle cation permeability (SP-Ca) is higher in slow-twitch muscles. Hindlimb suspension decreases SP-Ca and resting calcium, preceding functional changes and suggesting a calcium-dependent slow-to-fast muscle transition.
Area of Science:
- Muscle physiology
- Cellular calcium homeostasis
Background:
- Sarcolemmal permeability to cations (SP-Ca) differs between slow-twitch and fast-twitch muscles.
- Stretch-activated channels may contribute to higher SP-Ca in slow-twitch muscle.
- Hindlimb suspension (HU) induces muscle atrophy and functional changes.
Purpose of the Study:
- To investigate the changes in SP-Ca and resting calcium during HU.
- To determine if changes in SP-Ca and resting calcium precede functional alterations in slow-twitch muscle.
- To explore the role of calcium in the slow-to-fast muscle transition induced by HU.
Main Methods:
- Fura-2 fluorescence and manganese quenching technique to measure SP-Ca.
- Measurement of resting cytosolic calcium levels.
- Assessment of soleus muscle caffeine sensitivity and responsiveness.
- Comparison between soleus (slow-twitch) and extensor digitorum longus (EDL, fast-twitch) muscles.
Main Results:
- Slow-twitch muscles exhibit greater SP-Ca than fast-twitch muscles, linked to stretch-activated channels.
- HU induced significant, correlated decreases in soleus SP-Ca and resting calcium within 3 days.
- These calcium-related changes occurred before modifications in caffeine sensitivity or responsiveness.
- After 14 days of HU, soleus muscle SP-Ca, resting calcium, and caffeine response mimicked EDL muscle values.
Conclusions:
- Decreased SP-Ca and resting calcium precede functional adaptations in HU soleus muscle.
- Muscle shortening during HU may reduce SP-Ca, leading to lower resting calcium.
- The findings suggest that calcium-dependent mechanisms play a crucial role in the slow-to-fast transition of skeletal muscle phenotype during unloading.