Mechanical stimulation (forced circulation in narrow tubing) accelerates as much as 10-fold the rate of polymerization of actin. The increase in the rate is proportional to the intensity of the stimulation for flow rates between 0 and 3 cm/s. This supports the hypothesis that a statistical factor (the orientation of the flowing particles) is influenced by the flow. Comparison of the kinetics of the polymerization of resting and of mechanically stimulated actin solutions shows that both the nucleation and the elongation steps are accelerated. It is thus concluded that flow orients not only the oligomeric structures but also the actin monomers. The elongation reaction, also in the flow-stimulated samples, occurs always by the addition of ATP-G-actin (or ATP-containing oligomers) and not by the fusion of ADP-containing oligomeric structures.
