Enhanced resistance to fatigue and altered calcium handling properties of sarcalumenin knockout mice

Sarcalumenin is a Ca2+ binding protein located in the sarcoplasmic reticulum of striated muscle cells, the physiological function of which has not been fully determined yet. Using sarcalumenin knockout ( sar (-/-)) mice, we showed that sar ablation altered store- operated Ca2+ entry ( SOCE) and enhanced muscle fatigue resistance. Sar(-/-) mice fatigued less with treadmill exercise, and intact isolated soleus and extensor digitorum longus muscles from sar(-/-) mice were more resistant to intermittent fatiguing stimulation than those from wild- type mice. Enhanced SOCE was observed in the sar(-/-) muscles. Biochemical analysis revealed that sar(-/-) muscles contained significantly elevated expression of mitsugumin 29 ( MG29), a synaptophysin- related membrane protein located in the triad junction of skeletal muscle. Because the ablation of mg29 has been shown to cause increased fatigability and dysfunction of SOCE, the enhanced SOCE activity seen in sar(-/-) muscle may be correlated with the increased expression of MG29. Our data suggest that systemic ablation of sarcalumenin caused enhanced resistance to muscle fatigue by compensatory changes in Ca2+ regulatory proteins that effect SOCE.