Effects Of Hibernation On Fibre Type And Contractile Function In Ground Squirrel Soleus Muscle

Background:Therapy of bed-rest sufferer would be more difficult, time and efficiency of work and lifesaving ability of cosmonaut would be limited and threatened because of disused muscle atrophy. Therefore, disused atrophy has become one problem which must be solved urgently. To research the mechanism and reason of muscle atrophy not only have clinic benefit to curing muscle of long bed-rest patient for a long term, but also have important promotion role to spaceflight and sport medicine.Daurian ground squrrel (Citellus dauricus)is a species of typical rodent, its muscle is undoubtely under disused condition during months hibernation. Whereas, arousal from hibenation , ground squrrel whould not present obvious signs of muscle atrophy, such as limb disability, moving difficultly, even can't moving. Therefore, to study the changes of fibres type and contratile function in ground squrrel soleus muscle during hibernation can prove up mechamism of anti-atrophy of ground squrrel and provide new experimental data for musce physiology of hibernation. In addition, it also may create new ideal for prevention and treatment of muscle atrophy.Objective:Observe the changs of hemorheology, fibers type and contractile function in soleus muscle of ground squrrel during hibernation, study the effcts of hibernation on fibers type and contractile fnction in ground squrrel soleus muscleMethod:The m- ATPase activities in soleus muscle in ground squirrel during postnatal development was detected by m-ATPase histochemical method. (2) Fibre types in ground squirrel soleus muscle during hibernation were identified by immunity histochemistry technology with antibody fast-twitch myosin heavy chain(MHC). (3) Percentage of fibre types were measured by Motic Images plus 2.0 software. (4) Hemorheology of ground squirrel during hibernation was detected with blood viscosity instrument etc. (5) Contractile function in soleus muscle in ground squirrel during hibernation was observed using PowerLab system and electronical stimulator ,etc.Result:(1) The percentage of type II fibres in soleus muscle in young was obviously higher than in both sub-adult and adult ground squirrel (P<0.01). Furthermore, The percentage of type II fibres in soleus muscle in sub-adult was higher than that of adult(P= 0.059).(2) The whole viscosity at high shear rate of ground squirrel during hibernation didn't show significantly difference. However, the whole viscosity at both middle and low shear rates of ground squirrel of hibernation 1 month(H-lm)ere markedly higher than that of pre-hibernating ground squirrel (P<0.05). The both plasma viscosity and hematocrit (HCT) of ground squirrel during hibernation didn't present obviously changes (P>0.05). In addition, compared with pre-hibernating ground squirrel, the erythrocyte rigidity index (EIR) of individuals of H-1m, hibernation 2 month (H-2m) and hibernation 2.5 month (H-2.5m) increased 0.49%(P>0.05), 0.62%(P>0.05) and 6.87%(P>0.05), respectively. The mean EIR of ground squirrel of after hibernation for 1-2 days (AH) was 3.358±0.391, higher than that of pre-hibernating individuals, but lower than that of H-2.5m individuals (P>0.05).(3) The ratio of soleus muscle weight to body weight of pre-ground squirrel was 0.273±0.041, the ratio of individuals of H-1m, H-2m and H-2.5m decreased 0.94%(P>0.05), 7.10%(P>0.05) and 14.56%(P>0.05), respectively. The ratio of AH ground squirrel was 0.225±0.037, decreased 17.54%(P>0.05) compared with pre-hibernating individuals, but there was not significance.(4) The percentage of types I and II MHC fibres in soleus muscle in ground squirrel during hibernation didn't present significant variation(P>0.05). However, all the percentages of type I MHC fibres of individuals of H-1m, H-2m and H-2.5m were higher than pre-hibernating squirrel, even the H-2m individuals presented the most increased extent, increased 6.00%(P=0.092), showed a ascendant tendency. In addition, the percentage of type I MHC fibres of AH individuals was also higher than that of pre-hibernating individuals, but lower than that of individuals of H-1m, H-2m and H-2.5m.(5) The peak isometric twitch tension (Pt) in soleus muscle of pre-hibernating ground squirrel was (0.114±0.017) (g/mg). The H-1m individuals increased 10.42%(P>0.05), the individuals of H-2m and H-2,5m decreased 1.72%(P>0.05), 2.62%(P>0.05), respectively, furthermore, AH individuals decreased 5.93%(P>0.05). Compared pre-hibernating ground squirrel, the maximum tetanic tension (Po) of individuals of H-1m, H-2m and H-2.5m decreased 8.08%(P>0.05), 0.61%(P>0.05)and 5.07%(P>0.05),respectively. However, AH individuals increased 3.57%(P>0.05).(6) The time to 50% peak tension (TP₅₀) and time to peak tension (TPT) in ground squirrel soleus muscle during hibernation didn't present significant difference. Only the TPT of H-2m individuals showed ascendant tendency(P=0.078). However, the both 50% relaxation time (RT₅₀) and 75% relaxation time (RT75) showed obvious increase(P<0.05), the RT75 of H-2.5 m individuals especially(P<0.01).Conclusion(1)The percentage of type II fibres in soleus muscle in ground squirrel during postnatal development presented continuous decrease tendency, furthermore the change happened primarily during the development period of young to sub-adult.(2) The plasma viscosity, HCT and ERI of ground squirrel during hibernation didn't presented significant changes. However, whole blood viscosity at both middle and low shear rates of H-1m individuals obviously increased.(3) The ratio of soleus weight to body weight of ground squirrel during different hibernation period showed continuous decrease, but soleus muscle didn't presented marked atrophy characteristics according to its figure. (4) The fibre types in soleus muscle in ground squirrel during hibernation presented the transformational tendency of type IIMHC to type I MHC, furthermore the change wouldn't come back to the pre-hibernating condition during a short term.(5) The contractile tension in soleus muscle in ground squirrel during hibernation didn't present significant change.(6) The obvious change of isometric twitch during in soleus muscle in ground squirrel happened during hibernation, furthermore the change showed primarily the sign of relaxation time increase.