Local anesthetics are known to inhibit neuronal fast anterograde axoplasmic transport (FAAT) in a reversible and dose-dependent manner, but the precise mechanism has not been determined. FAAT is powered by kinesin superfamily proteins, which transport membranous organelles, vesicles, or protein complexes along microtubules. We investigated the direct effect of local anesthetics on kinesin, using both in vitro motility and single-molecule motility assays. In the modified in vitro motility assay, local anesthetics immediately and reversibly stopped the kinesin-based microtubule movement in an all-or-none fashion without lowering kinesin ATPase activity. QX-314, a permanently charged derivative of lidocaine, exerted an effect similar to that of lidocaine, suggesting that the effect of anesthetics is due to the charged form of the anesthetics. In the single-molecule motility assay, the local anesthetic tetracaine inhibited the motility of individual kinesin molecules in a dose-dependent manner. The concentrations of the anesthetics that inhibited the motility of kinesin correlated well with those blocking FAAT. We conclude that the charged form of local anesthetics directly and reversibly inhibits kinesin motility in a dose-dependent manner, and it is the major cause of the inhibition of FAAT by local anesthetics.
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