Direct inhibition of microtubule-based kinesin motility by local anesthetics

Local anesthetics are known to inhibit neuronal fast anterograde axoplasmic transport (FAAT) in a reversible and dose-dependent manner, but the precis e mechanism has not been determined. FAAT is powered by kinesin superfamily proteins, which transport membranous organelles, vesicles, or protein comp lexes along microtubules. We investigated the direct effect of local anesth etics on kinesin, using both in vitro motility and single-molecule motility assays. In the modified in vitro motility assay, local anesthetics immedia tely and reversibly stopped the kinesin-based microtubule movement in an al l-or-none fashion without lowering kinesin ATPase activity. QX-314, a perma nently charged derivative of lidocaine, exerted an effect similar to that o f lidocaine, suggesting that the effect of anesthetics is due to the charge d form of the anesthetics. In the single-molecule motility assay, the local anesthetic tetracaine inhibited the motility of individual kinesin molecul es in a dose-dependent manner. The concentrations of the anesthetics that i nhibited the motility of kinesin correlated well with those blocking FAAT. We conclude that the charged form of local anesthetics directly and reversi bly inhibits kinesin motility in a dose-dependent manner, and it is the maj or cause of the inhibition of FAAT by local anesthetics.