Premium
Hibernating black bears ( Ursus americanus ) maintain muscle to body weight ratio in unloaded soleus muscle
Author(s) -
Van Dyke Jonathan M,
Baewer David V,
Curry Brian D,
Govindaraju Sandya R,
Bain James W,
Vogel Valentine,
Riley Danny A
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a602-d
Subject(s) - soleus muscle , myofibril , skeletal muscle , hibernation (computing) , medicine , atrophy , anatomy , zoology , chemistry , endocrinology , biology , state (computer science) , algorithm , computer science
Black bears overwinter (hibernate) in dens for many months when food is scarce. Despite the extended period of reduced ambulatory activity, skeletal muscle exhibits little or no atrophy compared to that observed in human muscles unloaded for equivalent durations. The soleus muscle, which is the most sensitive to unloading in humans, has not been examined in bears. Our study compared soleus fiber type properties in biopsies from summer‐active adult and juvenile bears to those of bears after 4–5 months of hibernation. Muscle tissue was quick frozen for myofibrillar ATPase histochemical staining. Cross‐sectional areas and fiber type percentages were assessed morphometrically. The mean cross‐sectional fiber area to body weight ratio (mfa/bw) of summer adults was 24.1 ± 5.2 μm 2 /lb, and the soleus contained 89% slow, 1% intermediate and 11% fast fibers on average. Summer juveniles were not significantly different in mfa/bw (25.3 ± 6.0 μm 2 /lb), but the slow fiber percentage (81%) was lower than in adults. Hibernating adults exhibited no significant change in mfa/bw (23.4 ± 6.8 μm 2 /lb) and a slight reduction (3%) in slow fibers. These data demonstrate that bears maintain muscle mass during hibernation proportional to body weight and resist the negative effects of reduced weightbearing activity. Understanding this mechanism may help preserve skeletal muscle in humans in clinical bed rest and astronauts in microgravity.