an:05502980
Zbl 1153.92011
Walcott, Sam; Herzog, Walter
Modeling residual force enhancement with generic cross-bridge models
EN
Math. Biosci. 216, No. 2, 172-186 (2008).
00243379
2008
j
92C30 93A30 37N25
force enhancement; molecular history-dependence; stuck cross-bridge model; multi-cycle model; strain-dependent rate constants
Summary: The interaction of actin and myosin through cross-bridges explains much of muscle behavior. However, some properties of muscle, such as residual force enhancement, cannot be explained by current cross-bridge models. There is ongoing debate whether conceptual cross-bridge models, as pioneered by \textit{A. F. Huxley} [Muscle structure and theories of contraction. Prog. Biophys. Biophys. Chem. 7, 255 ff (1957)] could, if suitably modified, fit experimental data showing residual force enhancement.
We prove that there are only two ways to explain residual force enhancement with these `traditional' cross-bridge models: the first requires cross-bridges to become stuck on actin (the stuck cross-bridge model) while the second requires that cross-bridges that are pulled off beyond a critical strain enter a `new' unbound state that leads to a new force-producing cycle (the multi-cycle model). Stuck cross-bridge models cannot fit the velocity and stretch amplitude dependence of residual force enhancement, while the multi-cycle models can. The results of this theoretical analysis demonstrate that current kinetic models of cross-bridge action cannot explain the experimentally observed residual force enhancement. Either cross-bridges in the force-enhanced state follow a different kinetic cycle than cross-bridges in a `normal' force state, or the assumptions underlying traditional cross-bridge models must be violated during experiments that show residual force enhancement.