M.Sc Student | Abramovich Aviv |
---|---|
Subject | The Effect of Sarcomere Shortening Velocity on the Generated Force in Cardiac Fiber |
Department | Department of Biomedical Engineering | Supervisor | Professor Amir Landesberg |
The
hypothesis that cross-bridge (XB) transition rate (g) from the strong to the
weak state (weakening) depends on the shortening velocity (VSL),
, provides analytical solution for the force ? velocity relationship and
energy conversion by the sarcomere. The effect of VSL
on XB weakening was quantified in 6 trabeculae from the rat right ventricle,
using K-H solution, [Ca]o=1.5 mM, 25o C. Two protocols
were utilized: a) Identical VSL were imposed at various instants
during the twitch. b) Various amplitudes of VSL were imposed at the
same instant. Sarcomere length was measured with laser diffraction techniques.
The
response to shortening consisted of an initial exponential decline of force (F)
(t = 2 ms) followed by a slow decrease of F. The
instantaneous difference between the isometric F (FM) and F during
the second slow phase, depended on the shortening duration (Dt), the instantaneous FM and VSL:
where g1 was 1.189 ? 0.521 mm-1 (mean
? s.d.). F/FM was independent of the time onset of shortening but
exhibits the effect of VSL on the rate of XB weakening. The
propertionalty coefficient, g1, provides measurable time independent
index of muscle contractilty based on XB dynamics.?