Effect of unilateral denervation on maximum specific force in rat diaphragm muscle
fibers.
Geiger, Paige C., Mark J. Cody, Rebecca L. Macken, Megan. E. Bayrd, and Gary C.
Sieck.
Departments of Anesthesiology1 and Physiology & Biophysics2, Mayo Clinic
and Foundation, Rochester, Minnesota 55905
APStracts 7:0046A, 2000.
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
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 («minus»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 specific force
of fibers expressing MHC2X was reduced by ~40% (MHC2B expression was absent),
whereas the 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.
Received 25 July 2000; accepted in final form 17 October 2000
APS Manuscript Number A748-0.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2000 The American Physiological Society.
Published in APStracts on 29 January 2001