14 days of spaceflight or hindlimb suspension in rats increased the percentage of soleus muscle fibers with multiple myosin heavy chain isoforms from 6% in controls to 34% and 32%, respectively.
Does absence of weight bearing (spaceflight or hindlimb suspension) alter myosin heavy chain isoform content in rat soleus muscle?
Absence of weight bearing induces a shift toward type IIx MHC protein expression in preexisting type I and IIa fibers of the adult rat soleus muscle.
Absolute Event Rate: 34% vs 6%
The effects of 14 days of spaceflight (SF) or hindlimb suspension (HS) (Cosmos 2044) on myosin heavy chain (MHC) isoform content of the rat soleus muscle and single muscle fibers were determined. On the basis of electrophoretic analyses, there was a de novo synthesis of type IIx MHC but no change in either type I or IIa MHC isoform proportions after either SF or HS compared with controls. The percentage of fibers containing only type I MHC decreased by 26 and 23%, and the percentage of fibers with multiple MHCs increased from 6% in controls to 32% in HS and 34% in SF rats. Type IIx MHC was always found in combination with another MHC or combination of MHCs; i.e., no fibers contained type IIx MHC exclusively. These data suggest that the expression of the normal complement of MHC isoforms in the adult rat soleus muscle is dependent, in part, on normal weight bearing and that the absence of weight bearing induces a shift toward type IIx MHC protein expression in the preexisting type I and IIa fibers of the soleus.
Talmadge et al. (Sun,) conducted a other in Non-weight-bearing muscle adaptation. Spaceflight (SF) or hindlimb suspension (HS) vs. Controls was evaluated on Percentage of fibers with multiple myosin heavy chain (MHC) isoforms. 14 days of spaceflight or hindlimb suspension in rats increased the percentage of soleus muscle fibers with multiple myosin heavy chain isoforms from 6% in controls to 34% and 32%, respectively.