Length-dependent activation at high passive force in PLV. (A) Force–pCa curves at SL 1.9 and 2.3 μm, with high passive force at 2.3 μm (dashed lines). Left, control PLV (n = 6); right, sTn-reconstituted PLV (n = 6). Data obtained at steady-state passive force are taken from Fig. 1 C and shown by solid lines. Inset, ΔpCa₅₀ (High PF, high passive force). Bottom, passive force. *, P < 0.05 compared with the corresponding values obtained at steady-state passive force. (B), Relation between titin-based passive force and pCa₅₀ (left) (slope: 0.020 and 0.016, in control and sTn-reconstituted PLV, respectively) or maximal Ca²⁺-activated force (right) (slope: 3.407 and 2.690, in control and sTn-reconstituted PLV, respectively). ΔTitin-based passive force denotes difference between the values of titin-based passive force at SL 1.9 and 2.3 μm.