The response of compressed skinned skeletal muscle fibers to
conditions that simulate fatigue.
Myburgh, Kathryn H., and Roger Cooke.
Department of Biochemistry and Biophysics and the Cardiovascular
Research Institute, Box 0448, University of California at San
Francisco, San Francisco, CA 94143, USA, Tel: 415 - 476 4836, Fax:
415 - 476 1902
APStracts 3:0550A, 1996.
During fatigue muscles become weaker, slower, and more economical at
producing tension. Studies of skinned muscle fibers can explain some
but not all of these effects, and in particular they are less
economical in conditions that simulate fatigue. We investigated three
factors that may contribute to the different behavior of skinned
fibers. 1. Skinned fibers have increased myofilament lattice spacing,
which is reversible by osmotic compression. 2. A myosin subunit
becomes phosphorylated during fatigue. 3. IMP accumulates during
fatigue. We tested the response of phosphorylated and
unphosphorylated single skinned fibers (isometric tension,
contraction velocity, and ATPase activity) to changes in lattice
spacing (0 - 5% dextran) and IMP (0 - 5 mM) in the presence of
altered concentrations of Pi (3 - 25 mM), H+ (pH7 - 6.2) and ADP (0 -
5 mM). The response of maximally activated skinned fibers to the
direct metabolites of ATP hydrolysis is not altered by osmotic
compression, phosphorylating myosin subunits, or increasing IMP
concentration. These factors therefore do not explain the discrepancy
between intact and skinned fibers during fatigue.
Received 7 August 1996; accepted in final form 25 November 1996.
APS Manuscript Number A760-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996