Effects of anesthetics on ATPase activlty and motility of adomyosin dirrectly studied by in vitro motility assay.

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Using a recently developed in vitro motility assay, we have demonstrated that local anesthetics, lidocaine and tetracaine directly inhibit myosin-based movement of single actin filaments in a reversible dose-dependent manner. The inhibitory action of the local anesthetics on actomyosin sliding movement was pH dependent ; the anesthetics were more potent at higher pH values, and this reaction was accompanied by an increased proportion of the uncharged form of the anesthetics. QX-314, a permanently charged derivative of lidocaine, had no effect on actomyosin sliding movement. These results indicate that the uncharged form of local anesthetics is predominatly responsible for the inhibition of actomyosin sliding movement. The local anesthetic inhibited aliding movement but hardly interfered with the binding of actin filaments to myosin on the surface or with actomyosin ATPase activity at low ionic strength. To characterize the actomyosin interaction in the presence of anesthetics, we measured the binding and breaking force of the actomyosin complex. The binding of actin filaments to myosin on the surface was not affected by lidocaine at low ionic strength. The results suggest that the binding and ATPase of actomyosin are governed predominantly by ionic interaction, which is hardly affected by anesthetics ; whereas the force generation requires hydrophobic interaction, which plays a major part of the strong binding and is blocked by anesthetics, in addition to the ionic interaction.