Fiber size, type, and myosin heavy chain content in rhesus hindlimb muscles after 2 weeks at 2 G.
BACKGROUND
Fiber atrophy and an increase in the percentage of fast fibers have been observed in Rhesus leg muscles after spaceflight.


OBJECTIVE
Hypergravity will result in muscle fiber hypertrophy and an increase in the percentage of slow fibers.


METHODS
Open muscle biopsies were obtained from Rhesus soleus, medial gastrocnemius (MG), and tibialis anterior (TA) muscles before and after 14 d of centrifugation (2 G) and in time-matched controls. Cage activity levels were measured by telemetry.


RESULTS
Based on monoclonal antibody binding for myosin heavy chains (MHC), the fastest region of soleus contained a higher proportion of type I+II (27 vs. 13%) and had a tendency for a lower proportion of type I (38 vs. 61%, p = 0.10) fibers after than before centrifugation. There was a higher proportion of type I+II fibers in post- vs. pre-2 G (10 vs. 0.6%) MG biopsies. Fiber type distribution and MHC composition were unaffected in the TA. Overall, mean fiber sizes were unaffected by centrifugation. Average cage activity levels were 36% lower during than before 2 G.


CONCLUSIONS
Our hypothesis was rejected. The changes in the proportion of fibers expressing type I MHC are the reverse of that expected with chronic loading of extensors and, paradoxically, are similar to changes observed with chronic unloading, such as occurs during spaceflight, in this primate model. The data are consistent with the observed decrease in total daily activity levels.
Tavakol
Morteza
M
Department of Physiological Science, University of California, Los Angeles 90095-1761, USA.
Roy
Roland R
RR
Kim
Jung A
JA
Zhong
Hui
H
Hodgson
John A
JA
Hoban-Higgins
Tana M
TM
Fuller
Charles A
CA
Edgerton
V Reggie
VR
D000222:Adaptation, Physiological; D000818:Animals; D002498:Centrifugation; D006614:Hindlimb; D018471:Hypergravity; D007150:Immunohistochemistry; D008253:Macaca mulatta; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000473:pathology*; D018995:Myosin Heavy Chains / Q000032:analysis*
D018995:Myosin Heavy Chains