Fig. 1

Schematic illustration of state transition in the new hybrid contraction model. a Each state is denoted with reference to the composition of the state, namely, Ca²⁺ (c), actin (A), myosin (M), ATP (T), ADP (D), and inorganic phosphate (P or Pi), the weakly bound state of the crossbridge (CB) (w), and the strongly bound state of CB (s). The six states of the troponin system (TS, TSCa3, TSCa3 ^~, TSCa3 ^*, TS ^*, and TS ^~) in the original NL model [14] correspond approximately to those of the new hybrid model, as indicated above the new notations in a. A ₀–A ₃ indicates the corresponding four states of the reduced ATP hydrolysis model [5, 6]. The phenomenological rate constants Y, Z, f, and g are assigned to each step, as indicated. b Black lines Conformational change of the actin–actomyosin complex with and without Ca²⁺ binding, gray lines power stroke The flux of each transition is defined by Q ₁–Q ₁₃ as indicated