[Contribution of cooperative mechanisms of the thin filament activation to the myocardium contractile function. Assessment by a mathematical model].

We applied a mathematical model to compare the contributions to the myocardium mechanical activity of two a priori feasible variants of the cooperative effect of myosin cross-bridges on the calcium activation of sarcomere thin filaments. One of these variants implies that cross-bridge cooperative influence on the troponin C affinity to calcium is localized within the same functional cluster A7TmTn where the cross-bridge is attached. The second variant is based on the assumption that cross-bridges may affect the affinity of troponin C to calcium in other functional clusters A7TmTn as well (so that the nearer to the cross-bridge a cluster lies, the stronger the cross-bridge affects the affinity of CaTnC complex in this cluster). Each of these two variants and its contribution to the active mechanical performance of the heart muscle during the contraction-relaxation cycle were alternatively assessed in the model. It was found that only the second variant correctly simulates the mechanical activity of the muscle. Thus, the modeling suggests that just this variant of the cooperativity seems to be more feasible.