Fig. 8. Distribution of microtubule sliding velocities on thinner (left) and thicker (right) bundles at 1 mM ATP (0.9 mM MgATP) and low (A) and high (B) concentrations of Ca²⁺. The sliding velocities are shown at <10^–9 M Ca²⁺(open boxes), 10^–7 M Ca²⁺ (filled boxes), 10^–5 M Ca²⁺ (grey boxes) and 10^–4 M Ca²⁺ (dotted boxes). Mean sliding velocities ± s.d. (n=number of microtubules) are shown in each graph. Velocities of sliding between the two doublet bundles (Fig. 2) were larger than those of microtubule sliding on bundles shown in this figure. This difference might be due to a different ionic strength between the reactivating solution (for Fig. 2) and the sliding assay buffer (for Fig. 8).