Abstract
Gene expression levels of heat shock proteins (hsps) in the slow-twitch soleus and fast-twitch plantaris muscles of rats were determined after hindlimb suspension or spaceflight. Male rats were hindlimb-suspended for 14 d or exposed to microgravity for 9 d. The mRNA expression levels of hsp27, hsp70, and hsp84 in the hindlimb-suspended and microgravity-exposed groups were compared with those in the controls. The mRNA expression levels of the 3 hsps in the soleus muscle under normal conditions were higher compared with those in the plantaris muscle. The mRNA expression levels of the 3 hsps in the soleus muscle were inhibited by hindlimb suspension and spaceflight. The mRNA expression levels of the 3 hsps in the plantaris muscle did not change after hindlimb suspension. It is suggested that the mRNA expression levels of the 3 hsps are regulated by the mechanical and neural activity levels, and therefore, the decreased mRNA expression levels of hsps in the slow-twitch muscle following hindlimb suspension and spaceflight are related to a reduction in the mechanical and neural activity levels.
