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.