Distribution of myosin heavy chain isoforms in non-weight bearing
rat soleus muscle fibers.
Talmadge, Robert J., Roland R. Roy, and V. Reggie Edgerton.
Department of Physiological Science and Brain Research
Institute
APStracts 3:0407A, 1996.
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. Based on
electrophoretic analyses there was a de novo synthesis of IIx MHC,
but no change in either type I or IIa MHC isoform proportions after
either SF or HS compared to 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
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 towards IIx MHC protein expression in
the pre-existing type I and IIa fibers of the soleus.
Received 11 March 1996; accepted in final form 14 August 1996.
APS Manuscript Number A242-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996