|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.?