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[Calcium leak of sarcoplasmic reticulum induces degradation of troponin I in skeletal muscle fibers.] [Ariticle in Chinese]

LI Quan, WANG Yun-Ying, LI Hui, JIAO Bo, YU Zhi-Bin

Key Laboratory of Aerospace Medicine, Ministry of Education； Department of Aerospace Physiology, the Fourth Military Medical University, Xi'an 710032, China

Abstract

The troponin I subunit (TnI) was used as a molecular marker to explore the relationship between the resting intracellular Ca2+ concentration and myofibril degradation in muscle fibers. The isolated soleus muscle strips of rats were treated by caffeine and H2O2. Caffeine is an opener to increase the calcium release channel open probability of sarcoplasmic reticulum (SR) in contraction phase. H2O2 induces a calcium leak of SR calcium release channel in relaxation phase. The expression and degradation of TnI were detected by Western blot. The resting tension of tetanic contraction and expression of TnI were not changed, but the developed tension was lowered in isolated soleus muscle strips during 40 min of calcium-free Krebs perfusion. Low concentrations of caffeine (1 and 5 mmol/L) perfusion induced a transient increase in resting tension during fatigue period, but did not alter the extent of fatigue, recovery rate after fatigue and expression of TnI in muscle strips. High concentration of caffeine (10 mmol/L) perfusion induced a progressive increase in resting tension, a higher rate of fatigue and a decrease in recovery rate after fatigue in muscle strips. There was a detectable degradation of TnI in soleus after 10 mmol/L caffeine treatment. H2O2 perfusion facilitated a progressive increase in resting tension in a dosedependent manner, but did not influence the fatigue rate of tetanic contraction. The recovery rate after fatigue showed a quick resumption before decline during H2O2 perfusion. Degradation of TnI occurred in 5 and 10 mmol/L H2O2-treated soleus muscles. Since resting tension is dependent on intracellular Ca2+ concentration, the above-mentioned results suggest that SR Ca2+ leakage in relaxation phase may induce a degradation of TnI in skeletal muscle fibers.

Key words: troponin I; resting tension; developed tension; degradation

Received: 2008-12-01　　Accepted: 2009-03-31

Corresponding author: 余志斌　　E-mail: yuzhib@fmmu.edu.cn

Citing This Article：

LI Quan, WANG Yun-Ying, LI Hui, JIAO Bo, YU Zhi-Bin. [Calcium leak of sarcoplasmic reticulum induces degradation of troponin I in skeletal muscle fibers.] [Ariticle in Chinese] . Acta Physiol Sin 2009; 61 (3): 223-229 (in Chinese with English abstract).