Figure 2. Early phases of the isotonic velocity transient at different loads and the effect of P_i.

A and B, isotonic velocity transients (lower traces) following force steps (upper traces) to 0.75 and to 0.5 T₀ in the control (A) and in the presence of 10 mm P_i (B); middle traces, force baseline. C, superimposed isotonic velocity transients following a force step to 0.5 T₀ in control (black trace from A) and in 10 mm P_i (green trace from B). D, superimposed phase 2 transients in control (black trace) and in 10 mm P_i (green trace), obtained after subtracting phases 1 and 3 shortening as in Fig. 1C. E, relation of L₁ (circles) and L₂ (triangles) versus force in control (black symbols) and in 10 mm P_i (green symbols). F, relation between the shortening accounted for by the working stroke (L_T) and the force T (kPa) in control (black circles) and in 10 mm P_i (green circles). G, same relations as in F, with force expressed in relative units T/T₀. H, dependence of the rate constant of the working stroke (r₂) on force in control (black circles) and in 10 mm P_i (green circles). In panels E–H, data are the means ± SEM from the five fibres used in these experiments.