Effects Of Temperature And Oxygen Partial Pressure On The Contractile Properties Of Skeletal Muscle From Two Species Of Lizard At High And Low Altitude

The temperature and oxygen partial pressure are important factors affecting physiological activity of ectotherm.There are many researches about the effect of temperature on the contractile properties,and also about the effect of hypoxia on the locomotion ability.But the effect of hypoxia on skeletal muscle in vitro has not been reported.The red tail toad-headed lizard（Phrynocephalus erythrurus）is considered to be the highest living lizard in the world（mostly4500-5000 m above sea level）,which inhabits the Qiangtang Plateau in northern Tibet,suffering severe condition of cold and hypoxia over a long period of time.In order to research the effects of temperature and oxygen partial pressure on the contractile properties of skeletal muscle,the isometric and isotonic contractile properties of iliofibularis muscle（IF）and ATPase activity of gastrocnemius muscle in the lizards Phrynocephalus przewalskii and Phrynocephalus erythrurus were measured in vitro at 10,25,35,40,and 45°C.We also measured the contractile properties under different oxygen concentration,15 Torr and 40 Torr.Our analysis demonstrates that maximal velocity of shortening（Vmax）,maximal power output（P/m）,time-to-peak twitch tension（TPT）,time of half relaxation from peak twitch tension（1/2RT）,rate of rise of tetanic tension（dPo/dt）,and ATPase activity are temperature dependent in both species.Maximal twitch tension（Pt）and tetanic tension（Po）have a low or negative thermal dependent.The Vmax,P/m and ATPase activity increase with temperature from 10°C to 35°C,but decrease at 40°C and 45°C in both species.TPT and 1/2RT decrease with temperature from 10°C to 35°C,and approximately trend to be stable from 35°C to 45°C.P.erythrurus have a better performance in the rates of excitation and relaxation,shortening velocity and mechanical power at 10°C,but P.przewalskii perform better at the rates of force generation.In the hypoxia groups,P.erythrurus maintain better mechanical performance than P.przewalskii.These characteristics of P.erythrurus are considered to be necessary strategies in locomotion ability for living at high altitude and may effectively compensate for the negative influence of cold and low P_O2.