Abstract
The study tests the hypothesis that the transition rate (G) of the cardiac cross-bridge (XB) from the strong force generating state to the weak state is a linear function of the sarcomere shortening velocity \(\left( {V_{{\text{SL}}} } \right)\). Force (F) was measured with a strain gauge in six trabeculae from the rat right ventricle in K-H solution \(\left[ {\left( {{\text{Ca}}} \right.} \right]_0 = 1.5\;{\text{mM,}}\;{\text{25}}{}^ \circ \left. {\text{C}} \right)\). Sarcomere length (SL) was measured with laser diffraction techniques. Twitch F at constant SL and the F response to shortening at constant \(V_{{\text{SL}}} \) \(\left( {0 - 8\mu {\text{m/s;}}\Delta {\text{SL}}\;{\text{50 - 100}}\;{\text{nm}}} \right)\) were measured at varied times during the twitch. The F response to shortening consisted of an initial fast exponential decline \(\left( {\tau {\text{ = 2}}\;{\text{ms}}} \right)\), followed by a slow decrease of F. The instantaneous difference (ΔF) between the isometric F(FM) and F during the slow phase depended on the duration of shortening (Δt), the instantaneous F M and V SL. \(\Delta F = G_1 \cdot F_{\text{M}} \cdot \Delta t \cdot V_{{\text{SL}}} \cdot (1 - V_{{\text{SL}}} /V_{{\text{MAX}}} )\) where V MAX is the unloaded V SL and G1 was \(\begin{gathered} 6.15 \pm 2.12\mu {\text{m}}^{ - {\text{1}}} \;\left( {{\text{mean}} \pm {\text{s}}{\text{.d}}{\text{.;}}n = 6} \right). \hfill \\ \Delta F/F_M \hfill \\ \end{gathered} \) was independent of the time onset of shortening. The linear interrelation between \(\Delta F\) and V SL is consistent with the suggested feedback, whereby XB kinetics depends on V SL. This feedback provides a more universal description of the interrelation between shortening and force, as well as the observed linear relation between energy consumption and the mechanical energy output. © 2000 Biomedical Engineering Society.PAC00: 8719Hh, 8719Ff, 8719Rr
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Landesberg, A., Livshitz, L. & ter Keurs, H.E.D.J. The Effect of Sarcomere Shortening Velocity on Force Generation, Analysis, and Verification of Models for Crossbridge Dynamics. Annals of Biomedical Engineering 28, 968–978 (2000). https://doi.org/10.1114/1.1321013
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DOI: https://doi.org/10.1114/1.1321013