AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 1 56-R64, Copyright © 1986 by American Physiological Society
Elastic energy storage in rigored skeletal muscle cells under physiological loading conditions
J. G. Tidball and T. L. Daniel
The capability of heavy meromyosin (HMM) to store energy in reversible
deformations has been investigated previously; yet, whether HMM is the site
of most elastic energy storage in skeletal muscle cells has not been
established. We conducted dynamic loading tests on single rigored muscle
cells over the physiological range of sarcomere lengths. These tests
enabled us to calculate the energy stored in reversible deformations or
dissipated in the cell during each cycle of oscillation. Our findings show
that these cells are capable of storing approximately 0.5 J . kg-1 of
elastic energy during the last 50 ms of passive extension in vivo by
agonists and before their own active contraction. Possible sites of this
energy storage are HMM subunit 2, the proximal portion of HMM subunit 1,
and parallel structures. However, energy storage increases monotonically as
myofilament overlap decreases in the physiological range. This negative
correlation suggests that HMM subunits are not the primary sites of elastic
energy storage. Our electron-microscopic observations show that collagen
fibrils at the cell's surface become oriented parallel to the cell's long
axis over the range of sarcomere lengths where energy storage increases.
This provides a mechanism for the observed increases in elastic energy
storage.
