Insulin-like growth factor-I splice-variants expression and myosatellite cells in the rat m. soleus under unloading and passive stretch]

Hindlimb unloading produces atrophy and suppresses proliferative processes in postural muscles. Muscle stretch applied simultaneously with hindlimb suspension is known to prevent soleus muscle atrophy. In the rat experiments, we assessed the number of M-cadherin (satellite cell marker molecule)-labeled cells per one myofiber cross-section. After 2-week hindlimb suspension the number of labeled cells decreases by 33% as compared to the control group. The amount of labeled cells was 2.5-fold greater in passive stretch group in comparison with the hindlimb suspended animals and 1.7-fold greater as compared to the control group. We suppose that that proliferation of satellite cells with subsequent incorporation of their nuclei in myofiber is sufficient for increasing the protein synthesis. The insulin-like growth factor (IGF-I) is involved in regulation of protein turnover and exerts potent mitogenic and differentiating effects. We investigated the level of IGF-I expression in soleus muscle tissue after 14 day hindlimb suspension with stretch and observed no changes as compared to the control or 14 day hindlimb suspended group. We conclude that the muscle IGF-I and satellite cells incorporation do not make essential contribution to passive stretch preventive action under the conditions of simulated weightlessness.