Effect of short-term gravitational unloading on rat and mongolian gerbil muscles

Abstract

Gravitational unloading leads to destructive changes in the structure and function of muscle fibers. However, the role of the EMG activity level is still unclear. We measured changes caused by one- and three-day hypogravity in the following muscles: Soleus (Sol), Tibialis anterior (TA) and Gastrocnemius c.m. (MG). We used Wistar rats and Mongolian gerbils. The following parameters were assessed: the specific force of contraction of isolated fibers by tensometry, the transverse stiffness of the contractile apparatus by atomic force microscopy, and the calcium content by Fluo-4. We detected the accumulation of calcium ions in all muscles even after one-day unloading. In Sol this effect was more significant than in other muscles. After one-day of hypogravity we detected an increase in the specific force in all muscle types and species. Meanwhile, the transverse stiffness of the contractile apparatus, M-band and Z-disc increased only in fast muscles but not in Sol. After three-days of unloading, the specific force in Sol decreased, and the transverse stiffness of the contractile apparatus behaved in the same way as the force. The specific tension of fast muscle fibers decreased significantly in comparison with one-day unloading. In addition, the transverse stiffness of some areas of MG had a tendency to decrease in comparison to "one-day" unloading, although there was no such a tendency in the fibers of TA. In Mongolian gerbils the tendencies were the same as in the rats, but showed less dramatic changes. The reduction in the magnitude of changes in the Sol-MG-TA series correlates with EMG activity.

Desmin and α-actinin-2 content in rat soleus muscle in the dynamics of gravitational unloading and subsequent reloading

“…Our results on the relative content of desmin in functional unloading are consistent with the data described earlier [9,10]. In addition, the authors of [5] showed that, after gravitational unloading, the content of desmin in the rat vastus muscle decreased in the first day of suspending, remained below the control after 3 days, and almost completely restored on day 9.…”

“…Atrophy development is associated with degradation of cytosk eletal proteins, which is apparently induced by an increase in the concentration of calcium ions [6,9] and subsequent activation of calcium dependent pro teases calpains [5]. Substrates of the calpain pro teolytic system are important cytoskeletal proteins desmin and α actinin 2 [5].…”

Transversal Stiffness and Beta‐Actin and Alpha‐Actinin‐4 Content of the M. Soleus Fibers in the Conditions of a 3‐Day Reloading after 14‐Day Gravitational Unloading

“…Changes in the structure of muscle fibers, observed in a gravity disuse and follow-up readaptation period, naturally lead to a change in mechanical properties that depend on the integrity of the structure, such as stiffness. In turn, changes in the longitudinal and transversal stiffness are directly related to the changes in contractile properties of muscle fibers [12, 22, 23]. The results of the study of transversal stiffness of contractile apparatus suggest that gravitational unloading caused different changes in slow and fast muscles.…”

“…Structural basis of the transversal stiffness of the sarcolemma with cortical cytoskeleton is a network of filaments formed by nonmuscle actin-beta-actin. To form such a network, a host of capping proteins is needed, one of which is alpha-actinin-4, attention to which in a gravity disuse is due primarily to the fact that its binding to beta-actin depends on the content of calcium ions, the increase of which in these conditions has been shown previously [22, 24, 25]. …”

Automated rodent in situ muscle contraction assay and myofiber organization analysis in sarcopenia animal models

“…Those muscles with functional parameters, which deviated by Ͼ50% from the regression line, were also differentiated during the histological analysis. The agreement between functional and histological analysis demonstrates that the in situ assay system accurately reflects muscle functionality (24,27,40,44).…”