Fig. 6.

The ATP hydrolysis rate during the step experiment under the isotonic contraction mode. The external force was released from 60 to 30 mN/mm² (light gray), 15 mN/mm²(dark gray), and 5 mN/mm² (black) in panels a through d (200 ms). a F _ext, b halfSL, c v _ATPase, d h _p (upper traces) and h _w (lower traces), e phase L ₁–L ₄ of halfSL change on the expanded time scale (70 ms), f load–velocity (dh _p /dt) relation, g load–v _ATPase. In b the notation of the different phases of relaxation, L ₁–L ₄, are indicated in e (F _ext 60 → 5 mN/mm²). The [Ca²⁺] was 0.647 µM. a–d The gradation in color from gray to black is used to refer to the step size of F _ext, as indicated in a, during the test pulse. The relaxation rate in f and g, measured between 79 and 80 ms, was plotted against F _ext on the x-axis