(30) Remarks on Muscle Contraction Mechanism II. Isometric Tension Transient and Isotonic Velocity Transient
Toshio Mitsui, Nobukatsu Takai and Hiroyuki Ohshima
International Journal of Molecular Sciences，Vol.12，pp.1697-1726，2011
Mitsui and Ohshima (2008) criticized the power-stroke model for muscle contraction and proposed a new model. In the new model, about 41% of the myosin heads are bound to actin filaments, and each bound head forms a complex MA3 with three actin molecules A1, A2 and A3 forming the crossbridge. The complex translates along the actin filament cooperating with together. The new model well explained the experimental data on steady filament sliding. As an extension of the study, the isometric tension transient and isotonic velocity transient are investigated. Statistical assembly of crossbridges is introduced, and variation of the binding probability of myosin head to A1 is considered. When the binding probability to A1 is zero, the Hill-type force-velocity relation results. When the binding probability to A1 becomes finite, the deviation from the Hill-type force-velocity relation takes place, as observed by Edman (1988). The characteristics of the isometric tension transient observed by Ford, Huxley and Simmons (1977) and of the isotonic velocity transient observed by Civan and Podolsky (1966) are theoretically reproduced. Ratios of the extensibility are estimated as 0.22 for the crossbridge, 0.26 for the myosin filament and 0.52 for the actin filament, consistent with the values determined by X-ray diffraction by Wakabayashi et al. (1994).
>>
NEXT