Synergistic ablation does not affect atrophy or altered myosin heavy chain expression in the non-weight bearing soleus muscle.
The purpose of this study was to investigate whether the soleus muscle undergoes atrophy and alterations in myosin heavy chain (MHC) composition during non-weight bearing in the absence of synergists. Thirty-two female rats were randomly assigned to four groups: control (C), synergistic ablation (ABL) of the gastrocnemius and plantaris muscles to overload the soleus muscle, hindlimb suspension (HLS), or a combination of synergistic ablation and hindlimb suspension (HLS-ABL). After 28 days of hindlimb suspension, soleus atrophy was more pronounced in HLS (58%) than in HLS-ABL (43%) rats. Compared to C rats, non-weight bearing decreased mixed and myofibrillar protein contents and Type I MHC 49%, 45%, and 7%, respectively, in HLS animals. In addition, de novo expression of fast Type IIx and Type IIb MHC (5% and 2%, respectively) was observed in HLS animals. Similarly, when compared to C rats, mixed and myofibrillar protein contents and Type I MHC decreased 43%, 46%, and 4%, respectively, in HLS-ABL animals. Also, de novo expression of Type IIx (4%) and IIb (1%) MHC was observed. Collectively, these data indicate that the loss of muscle protein and Type I MHC, and the de novo expression of Type IIx and Type IIb MHC in the rat soleus occur independently of the presence of synergists during non-weight bearing. Furthermore, these results confirm the contention that soleus mass and MHC expression are highly sensitive to alterations in mechanical load.
Linderman
J K
JK
Life Science Division (239-11), NASA/Ames Research Center, Moffett Field, CA 94035-1000, USA.
Talmadge
R J
RJ
Gosselink
K L
KL
Tri
P N
PN
Roy
R R
RR
Grindeland
R E
RE
D000818:Animals; D001284:Atrophy; D005260:Female; D007103:Immobilization; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley; D016474:Weight-Bearing
D009124:Muscle Proteins; D018995:Myosin Heavy Chains