The study was aimed at investigating the mechanisms and structures which determine mechanical properties of skeletal muscles under gravitational unloading and plantar mechanical stimulation (PMS). We hypothesized that PMS would increase NO production and prevent an unloading-induced reduction in skeletal muscle passive stiffness. Wistar rats were hindlimb suspended and subjected to a How to cite this article: Tyganov SA, Mochalova EP, Melnikov IY, et al. NOS-dependent effects of plantar mechanical stimulation on mechanical characteristics and cytoskeletal proteins in rat soleus muscle during hindlimb suspension. FASEB

In mammals, prolonged mechanical unloading results in a signi cant decrease in passive stiffness of postural muscles. The nature of this phenomenon remains unclear. The aim of the present study was to investigate possible causes for a reduction in rat soleus passive stiffness after 7 and 14 days of unloading (hindlimb suspension, HS). We hypothesized that HS-induced decrease in passive stiffness would be associated with calpain-dependent degradation of cytoskeletal proteins or a decrease in actomyosin interaction. Wistar rats were subjected to HS for 7 and 14 days with or without PD150606 (calpain inhibitor) treatment. Soleus muscles were subjected to biochemical studies and ex vivo measurements of passive tension with or without blebbistatin treatment (an inhibitor of actomyosin interactions). Passive tension of isolated soleus muscle signi cantly reduced after 7-and 14-day HS compared to control values. PD150606 treatment during 7-and 14-day HS induced an increase in alphaactinin-2 and − 3, desmin contents compared to control, partly prevented a decrease in intact titin (T1) content and prevented a decrease in soleus passive tension. Incubation of soleus muscle with blebbistatin did not affect HS-induced reductions in speci c passive tension in soleus muscle. Our study suggests that calpain-dependent breakdown of cytoskeletal proteins, but not a change in actomyosin interaction, signi cantly contributes to unloading-induced reductions in intrinsic passive stiffness of rat soleus muscle.

In mammals, prolonged mechanical unloading results in a significant decrease in passive stiffness of postural muscles. The nature of this phenomenon remains unclear. The aim of the present study was to investigate possible causes for a reduction in rat soleus passive stiffness after 7 and 14 days of unloading (hindlimb suspension, HS). We hypothesized that HS-induced decrease in passive stiffness would be associated with calpain-dependent degradation of cytoskeletal proteins or a decrease in actomyosin interaction. Wistar rats were subjected to HS for 7 and 14 days with or without PD150606 (calpain inhibitor) treatment. Soleus muscles were subjected to biochemical studies and ex vivo measurements of passive tension with or without blebbistatin treatment (an inhibitor of actomyosin interactions). Passive tension of isolated soleus muscle significantly reduced after 7- and 14-day HS compared to control values. PD150606 treatment during 7- and 14-day HS induced an increase in alpha-actinin-2 and − 3, desmin contents compared to control, partly prevented a decrease in intact titin (T1) content and prevented a decrease in soleus passive tension. Incubation of soleus muscle with blebbistatin did not affect HS-induced reductions in specific passive tension in soleus muscle. Our study suggests that calpain-dependent breakdown of cytoskeletal proteins, but not a change in actomyosin interaction, significantly contributes to unloading-induced reductions in intrinsic passive stiffness of rat soleus muscle.