title: Time course changes in [Ca2+]i, force, and protein content in hindlimb-suspended mouse soleus muscles.
abstract: BACKGROUND
  Exposure to reduced gravitational forces during spaceflight is associated with significant reductions in skeletal muscle mass and strength. The purpose of this study was to test the hypothesis that increases in resting cytosolic free calcium concentration ([Ca2+]i) would precede reductions in protein content and maximal isometric tetanic force (Po) in mouse soleus muscle after initiation of hindlimb suspension.
  
  
  METHODS
  Female ICR mice (n = 42) were hindlimb suspended for 1, 2, 3, 5, or 7 d; weight-matched mice were used as controls. Following the hindlimb suspension, the left soleus muscle was used to determine Po in vitro and the right soleus muscle was used to determine protein content and [Ca2+]i via confocal laser scanning microscopy.
  
  
  RESULTS
  Compared with controls, [Ca2+]i was elevated by 38% at 2 d, and 117% at 7 d. Compared with controls, soleus muscle total and myofibrillar protein contents were reduced 27-29% and 30-34%, respectively, at 5-7 d after initiation of hindlimb suspension. Compared with controls, soleus muscle Po was decreased by 24% at 3 d, and 38% at 7 d.
  
  
  CONCLUSIONS
  It appears that resting cytosolic Ca2+ homeostasis is disturbed soon after the initiation of hindlimb suspension, and these elevations in [Ca2+]i may play a role in initiating soleus muscle atrophy.
authors.affiliation: Department of Health & Kinesiology, Texas A&M University, College Station, USA. cingalls@gsu.edu
authors.forename: C P
authors.initials: CP
authors.lastname: Ingalls
authors.forename: J C
authors.initials: JC
authors.lastname: Wenke
authors.forename: R B
authors.initials: RB
authors.lastname: Armstrong
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006801:Humans; D018472:Hypogravity / Q000009:adverse effects*; D007537:Isometric Contraction / Q000502:physiology*; D051379:Mice; D008813:Mice, Inbred ICR; D009124:Muscle Proteins / Q000032:analysis; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D009929:Organ Size; D013997:Time Factors
chemical_list: D009124:Muscle Proteins; D002118:Calcium