Stretch of Muscle Preserves Z-disc Structure in Unloaded Soleus

Objective To explore the effects of passive stretch on preserving Z-disc structure in unloaded soleus muscle Methods Forty rats were equally divided to control(Con),control with stretch(Con + stretch),tail-suspension(TS) and tail-suspension with stretch(TS+stretch).The tail-suspended rat model was used to induce an unloading of soleus muscle for 2 weeks.Left ankle of rat was fixed by a plaster cast at 35° of dorsiflexion.The soleus muscle was passively stretched in the fixed hind-limb.The changes of wet weight and ultrastructure of soleus muscle were examined.Results Compared with Con group,the ratio of soleus wet weight to body weight was decreased in the stretched muscle of Con+stretch group;the relative weight of soleus was further decreased in TS group.The decrease in the relative weight of soleus was partially reversed in the stretched muscle of TS+stretch group.The width of myofibril and Z-disc showed a trend toward reduction in soleus fibers of Con+stretch group and decreased significantly in TS group as compared with the Con group.The lengths of sarcomere and I-band were increased,but the length of A-band was unaltered in the TS group.The Z-disc showed a wavy appearance in TS group.Passive stretch in the unloaded soleus muscle restored normal appearance of Z-disc.The lengths of sarcomere,I-band,and A-band were unaltered.The widths of myofibril and Z-disc were also preserved at the levels of control soleus muscle.Conclusion These results indicate that passive stretch can prevent partially atrophy and preserve the Z-disc structure in the unloaded soleus muscle.