Nov 3 (Thursday) Walter Herzog (University of Calgary)

Considerations on history dependence of skeletal muscle contraction

Abstract:

It has been known for about half a century that the steady state
isometric force following stretch of an activated muscle is
substantially greater than the corresponding steady state force obtained
from a purely isometric contraction at the same length. However, the
mechanism(s) underlying this so called steady state or residual force
enhancement are not understood. We have studied force enhancement on a
variety of structural levels including in vivo human muscles, isolated
muscles and single fibres and myofibrils. Our results seem to indicate
that force enhancement is composed of at least two components, a passive
and an active component. We speculate that the passive component might
be associated with a calcium induced increase in the stiffness of the
molecular spring titin, and that the active component might be caused by
a decrease in Huxley's rate constant for cross-bridge detachment (g(x).
We hope to show in the future that the molecular interaction of myosin
II with actin has a memory for stretch that influences subsequent
actin-myosin interactions.