The Mechanism That Effect Of Hypoxia And Hypoxic Exercise On Titin And Nebulin Of Skeletal Muscle

Purposes:To investigate the mechanism that the effect of hypoxia and hypoxic exercise on titin and nebulin of skeletal muscle,the adaptation of hypoxia and hypoxic exercise on titin and nebulin of skeletal muscle and the differences of hypoxic exercise on titin and nebulin of digitorum longus and soleus.Methods:Male SD rats fell into three parts:chronic hypoxia and hypoxic exercise(12.7%oxygen concentration,train increasing load progressively on treadmill of 10 degree for 4 weeks),hypoxic stress(10% oxygen concentration,7 days),and acute hypoxic exercise(12.7%oxygen concentration,train intermittently on treadmill of 10 degree for 30 minutes,recovery in normal oxygen concentration and 12.7%oxygen concentration for 7 days).Gastrocnemius muscle,extensor digitorum longus and soleus were collected.The content of titin and nebulin of gastrocnemius muscle was determined by Western blotting.The mRNA expression of titin and nebulin was detected by real-time quantitative PCR.MDA and Calpain 1 & 2 activity were measured respectively by reagent kit.Results:(1) chronic hypoxia and hypoxic exercise:the content of titin of gastrocnemius muscle decreased markedly the first week(P＜0.05), the content of nebulin also decreased(P＞0.05),and gradually recovered the fouth week.mRNA level of titin and nebulin was similar to the content of titin and nebulin.(2) hypoxic stress:the content of nebulin of gastrocnemius muscle decreased remarkably from the first day to the seventh day(P＜0.05),the content of titin decreased from the second day to the seventh day;the content of MDA and the content of caspase-3 increased remarkably from the second day to the seventh day(P＜0.05), and the Calpain 1 & 2 activity increased from the frist day to the seventh day.(3) acute hypoxic exercise:the content of titin of gastrocnemius muscle decreased markedly the frist day(P＜0.05).the content of nebulin was not significantly decreased(P＜0.05);the content of MDA and caspase-3 and the Calpain 1 & 2 activity increased the first day,and then went down steadily.The content of titin of soleus decreased notablely right after hypoxic exercise(P＜0.05),the content of titin of extensor digitorum longus decreased remarkably the second day after hypoxic exercise (P＜0.05),the content of nebulin of extensor digitorum longus and soleus decreased markedly right after hypoxic exercise(P＜0.05).Conclusion:the mechanism of degradation of titin and nebulin during the hypoxia and hypoxic exercise was that Calpain 1 & 2 activity and caspase-3 make sarcomere damaged.Titin and nebulin might adapt to the hypoxia and hypoxic exercise.The effect of hypoxia and hypoxic exercise on titin and nebulin of digitorum longus and soleus differ.