ISSN:
1573-9686
Keywords:
Excitation contraction coupling
;
Force-velocity relation
;
Force deficit
;
Attachment–detachment
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
,
Technology
Notes:
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
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1114/1.1321013
Permalink
