Effects of tail suspension upon the morphology and myosin ATPase activities of the soleus muscle of the Dauria ground squirrel Spermophilus dauricus

摘要

Abstract The wet weig ht and the cross-section area (CSA) of the dauria ground squirrel’s soleus muscle were measured after 14 days’ tail suspension, and compared with those of tail-suspended rat. Meanwhile, myosin adenosine triphosphatase (mATPase) activities of intrafusal and extrafusal fibers in soleus were also detected and then compared with its corresponding control. These aimed to explore effects of tail suspension on morphology, microstructure, mATPase activities of intrafusal and extrafusal fibers in the soleus muscle of ground squirrels under conditions of muscle disuse. In rats , compared with the control group, the 14 d tail suspension group showed a significant difference in the ratios of wet muscle weight to body weight, decreasing 35.52% ( P <0.001); the CSA of type I and type II fibers decreased 18.91% and 20.68% ( P <0.05) respectively; the average CSA decreased 20.45%. The constituent ratio of type I fibers decreased from 80.61% to 66.83%, while that of type II fibers rose from 19.39% to 33.17% ( P <0.001). The activities of mATPase of intrafusal fibers exhibited higher histochemical activities after 14 days of tail suspension. Bag 1 intrafusal fibers of the rat showed strong activity (+++) as compared with the control group, Bag 2 intrafusal fibers and chain fibers showed strong activity (+++) instead of intermediate activity (++). In tail-suspended ground squirrels , the ratio of wet muscle weight to body weight only decreased 0.05%, while CSA of type I, II fibers and average CSA decreased 0.84%, 0.63% and 0.37%, respectively. There were no significant differences, compared with controls. The ratio of type I fibers decreased to 77.30%, as compared with the control (82.55%), while that of type II fibers increased from 17.45% to 22.70% ( P <0.05). mATPase activity of intrafusal fibres in tail-suspended ground squirrels also changed. Bag 1 intrafusal fibers showed strong activity (+++) compared with negative ( － ) of the controls, Bag 2 intrafusal fibers retained intermediate activity (++). Chain fibers retained intermediate activity (++) or showed weak activity (+) compared to controls. We conclude that, tail suspension might lead to significant muscle atrophy only in the rat; after 14 days of tail suspension, the mATPase activities of intrafusal and extrafusal fibers in the soleus muscle all increased both in the rat and in the ground squirrel [ Acta Zoologica Sinica 53(1): 116 – 122, 2007] .