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Departments of 1 Anesthesiology and 2 Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905
We hypothesize that 1) the
effect of denervation (DNV) is more pronounced in fibers expressing
fast myosin heavy chain (MHC) isoforms and 2) the effect of
DNV on maximum specific force reflects a reduction in MHC content per
half sarcomere or the number of cross bridges in parallel.
Studies were performed on single Triton X-100-permeabilized fibers
activated at a pCa (
log Ca2+ concentration) of 4.0. MHC
content per half sarcomere was determined by densitometric analysis of
SDS-PAGE gels and comparison to a standard curve of known MHC
concentrations. After 2 of wk DNV, the maximum specific force of fibers
expressing MHC2X was reduced by ~40% (MHC2B
expression was absent), whereas the maximum specific force of fibers
expressing MHC2A and MHCslow decreased by
only ~20%. DNV also reduced the MHC content in fibers expressing
MHC2X, with no effect on fibers expressing
MHC2A and MHCslow. When
normalized for MHC content per half sarcomere, force generated by DNV
fibers expressing MHC2X and MHC2A was decreased
compared with control fibers. These results suggest the force per cross
bridge is also affected by DNV.
inactivity; skinned fibers; myosin heavy chain content; force per cross bridge
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