dj-1 ( ~20 kda ) , also called park7 and cap-1 , is a small conserved protein associated with 
 autosomal - recessive early onset parkinson s disease1,2,3 .
the human dj-1 protein contains 189 amino acid residues1,2,3 and acts as a redox sensor , which the thiol 
 group of cysteines of dj-1 can be oxidized to soh , s2oh , and s3oh4,5,6 .
it was proposed that dj-1 may prevent 
 reactive oxygen species ( ros ) accumulation by regulating the levels of other antioxidants . 

furthermore , dj-1 has multiple cellular functions such as transcriptional regulation , 
 protease or redox - dependent chaperone activity , apoptosis and sumoylation5,6,7,8 , all 
 of which have been shown to play a role in skeletal muscle activity
. therefore , dj-1 appears 
 to be an important player in skeletal muscle function during the life - span , although its 
 mechanistic roles are yet to be determined .
skeletal muscle atrophy has proven to be a 
 significant orthopedic problem in the area of physical therapy9,10,11 .
muscle atrophy has generally been reported that 
 immobilization - induced atrophy , especially of physiotherapeutic area , decreased muscle 
 volume via decrease of contractile proteins , resulting in muscle weakness and disorder of 
 activities of daily living ( adl)9 , 10 , 12 , 13 . in our previous study , it was 
 demonstrated that cast - immobilization- and undernutrition - induced atrophy are correlated 
 with each other via dj-1 protein in skeletal muscle13 . furthermore , electrical properties such as rheobase and chronaxie 
 are important factors in electrodiagnosis by physiotherapists for measurement of muscle 
 degeneration such as total or partial muscle paralysis14 , 15 .
rheobase is measured as 
 the threshold stimulus current for an active response with a long - duration pulse and 
 chronaxie is the pulse width at twice the rheobase threshold current14 , 15 .
however , the 
 tendency of change in electrical activities on knockout of dj-1 is not fully understood . 

therefore , in the present study , the electrical properties of the gastrocnemius muscle of 
 dj-1 knockout ( dj-1 ) and wild - type ( dj-1 ) mice were 
 compared .
male dj-1 homozygous knockout ( dj-1 , b6.cg-park7tm1shn/j , 2530  g ; n=6 ) and 
 wild - type ( dj-1 ; n=6 ) mice with the same background were purchased from 
 jackson laboratory13 ( bar harbor , me , 
 usa ) . to confirm dj-1 gene depletion in mice , the distal tips of tails were obtained from 
 dj-1 and dj-1 mice .
genotyping using polymerase chain reaction 
 for dj-1 confirmation was performed with the following primers : dj-1 forward , 
 5-gct gaa act gtg cca tgt ga-3 ; dj-1 reverse , 5-tgc taa agc gca tgc tcc aga ct-3 ; mutant 
 neo , 5-tgg atg tgg aat gtg tgc gag-3. the expression of dj-1 protein was confirmed in 
 aortic strips using western blotting analysis13 , 
 16 , 17 .
our investigation conformed to the guide for the care and use of 
 laboratory animals published by the us national institutes of health ( nih publication no . 
 85 - 23 , revised 1996 ) , and all experiments and animal care conformed to the institutional 
 guidelines established by konkuk university , korea .
the animals were sacrificed using 
 co2 inhalation and gastrocnemius skeletal muscles were removed rapidly and 
 carefully from the limbs of animals and placed in cold krebs solution ( containing , in  mm : 
 nacl , 118.0 ; kcl , 4.8 ; cacl2 , 2.5 ; mgso4 , 1.2 ; nahco3 , 
 24.9 ; glucose 10.0 ; kh2po4 1.2 ) with 95% o2 and 5% 
 co2 mixed gas13 .
rheobase 
 and chronaxie were measured at the regions of the gastrocnemius muscles using an electrical 
 stimulator ( duo 500 , gymnauniphy co. , belgium ) .
a rheobase measurement pad was applied to 
 the regions of the gastrocnemius muscles of animals until the muscle contraction response 
 became visible14 , 15 .
the statistical 
 evaluation of data , using graphpad prism ( graphpad software , san diego , ca , usa ) , was 
 performed using student s t - tests for group comparisons and anova for multiple comparisons . 

the rheobase of dj-1 knockout mice showed a significant increase in a time - dependent 
 manner , compared to that of the wild - type mice ( n=6 ; table 1table 1.differences in the rheobase of dj-1 and dj-1 mouse 
 gastrocnemius musclesst(ms)rheobase ( ma)s(ms)rheobase ( ma)dj-1dj-1dj-1dj-10.13.60  0.145.93  0.84501.37  0.052.12  0.290.22.58  0.084.35  0.69701.37  0.052.12  0.290.52.12  0.113.50  0.481001.37  0.052.10  0.2911.55  0.102.47  0.382001.37  0.052.10  0.2921.37  0.052.22  0.263001.37  0.052.10  0.2951.37  0.052.13  0.285001.37  0.052.10  0.29101.37  0.052.12  0.297001.37  0.052.08  0.29201.37  0.052.12  0.291,0001.37  0.052.07  0.30301.37  0.052.12  0.29 - --mean  standard error .
st : stimulative time . * significantly different from 
 dj-1 for controls with p<0.05 . ) .
st : stimulative time . * significantly different from 
 dj-1 for controls with p<0.05 .
the skeletal muscle is tissue that has high potential plasticity and comprises 
 approximately 40% of the total body weight9 , 11 .
maintenance of muscle volume and function 
 is important for healthy life , and is important in the rehabilitation of musculoskeletal 
 disease in the field of physical therapy10 , 11 , 13 .
however , as muscle mass decreases , there is an accompanying loss of 
 muscle strength and use of nutrients which contributes to reduced muscle function and 
 quality of adl18,19,20,21 .
previous studies and our reports using a model of disuse atrophy 
 induced by cast immobilization indicated loss of muscle mass and cross - sectional area due to 
 a decrease in the rate of protein synthesis9,10,11 . 

the increased degradation of proteins in muscle atrophy is widely coupled with activation of 
 protein ligases such as muscle - specific ring finger-1 ( murf-1 ) and the muscle atrophy f - box 
 protein ( mafbx , also called atrogin-1)9,10,11 . 

our previous data showed that the first to describe the protective functions of dj-1 against 
 skeletal muscle atrophy are correlated with the mapk - ubiquitin ligase ( both murf-1 and 
 atrogin-1 ) pathway13 . in the present 
 study , it was found that dj-1 increased the rheobase in a time - dependent 
 manner .
based on these results , it is cautiously speculated that the increment in the 
 rheobase of dj-1 mice aids in decrease of neuromuscular activities and 
 disorder of movements . this result is similar to that of a previous study that reported that 
 24-month - old dj-1 mice showed shorter stride lengths than wild - type mice22 .
moreover , dj-1 mice exhibit 
 loss of ca homeostasis , such that decrease in depolarization evoked 
 ca release from the sarcoplasmic reticulum in the dj-1 null muscle cells , 
 implying that dj-1 plays a critical role in calcium regulation of skeletal muscle cells23 . however , further systematic and 
 scientific studies in the fields of physical therapy , such as exercise therapy , 
 electrotherapy , neurophysiotherapy , and hydrotherapy , are needed to confirm the mechanisms 
 underlying the effects of dj-1 in atrophied muscle strips and cells24,25,26,27 . in summary ,
the 
 rheobase of dj-1 knockout mice was significantly higher than that of wild - type mice .
the 
 present results suggest that dj-1 affects the important play a role in muscle activity13 , 22 , 23 , 26 .
 [ purpose ] strength - duration ( sd ) curves are used in electrical diagnosis by 
 physiotherapists to confirm muscle degeneration . 
 however , the usefulness of sd curves in 
 comparing muscle degeneration in dj-1 homozygous knockout ( dj-1/ ) and 
 wild - type mice ( dj-1+/+ ) is not yet fully understood . 
 the electrical properties 
 of the gastrocnemius muscles of dj-1/ and dj-1+/+ mice were 
 compared in the current study . 
 [ subjects and methods ] the electrode of an electrical 
 stimulator was applied to the gastrocnemius muscle to measure the rheobase until the 
 response of contractive muscle to electrical stimulation became visible in mice . 
 [ results ] 
 the rheobase of dj-1/ mice showed a significant increase in a time - dependent 
 manner , compared to that of dj-1+/+ mice . 
 [ conclusion ] these results 
 demonstrate that the dj-1 protein may be implicated in the regulation of neuromuscular 
 activity of gastrocnemius muscles of mice . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION