5.　How does the antigravity soleus muscle adapt to long-term stay on the Mars and the Moon?　Estimation using rat study

一般演題

「重力・水浸」

Y. Ohira^1,2, D. Uyeno¹, K. Kamibayashi¹, T. Ohira³, F. Kawano⁴, K. Goto⁵, H. Kato¹, H. Takakura^1,2, and T. Izawa^1,2

¹Fac. Health & Sports Sci.
²Res. Ctr. Adipocyte Muscle Sci., Doshisha Univ.
³Dept. Molcul. Physiol., Jikei Univ. Sch. Med.
⁴Grad. Sch. Health Sci., Matsumoto Univ.
⁵Grad. Sch. Health Sci., Toyohashi SOZO Univ., Japan

Responses of the properties in rat soleus muscle to inhibition of mechanical stress, equivalent to that in 1/3-G or 1/6-G environment were studied.　Responses to the simulation model of microgravity exposure were also examined.　The degree of mechanical stress was modified keeping the dorsal ankle joint at a certain level with or without plaster fixation during hindlimb suspension.　Body and muscle weights, as well as fiber CSA in soleus, were lowered following 10 days of hindlimb suspension of male Wistar Hannover rats keeping the soleus at a shortened length with or without fixation of ankle joint.　Significant decrease in the percent slow fibers was noted in the 120° and free joint groups and increase of fast fibers in the 120° group.　Greater decrease in the expression level of slow MHC protein was also seen in the 120°, 160°, and free joint groups.　Further, suspension-related decreases in citrate synthase activity and cytochrome c protein were observed, even in the 30° group.　The total activities of SDH analyzed in the cross-sections of single muscle fibers were decreased proportionally to fiber atrophy.　But its specific activities in slow and hybrid fibers were negatively correlated to the fiber CSA, suggesting that the degree of fiber atrophy was greater than that of the decrease of SDH level.　It was suggested that the chronic reduction of mechanical stress applied to the muscle to approximately 1/3 of normal level in 1-G environment could be critical for maintenance of morphological and metabolic properties of antigravity muscle, soleus.