Block of fast axonal transport in vitro by the local anesthetics dibucaine and etidocaine.

Other investigators have shown that procaine, lidocaine and tetracaine block fast axonal transport in vitro. The present study shows that dibucaine and etidocaine also exhibit this effect. The biological material used consists of the 8th and 9th dorsal root ganglia and spinal nerves of the bullfrog; in vitro fast transport of [3H]leucine-labeled proteins is quantitated by liquid scintillation counting. Exposure of spinal nerves to dibucaine reduces the quantity of 3H-proteins which is transported to a ligature by 72% at 0.5 mM and by greater than 90% at a 1 mM concentration; since 1 mM tetracaine reduces it by 64%, dibucaine is approximately twice as potent as tetracaine at inhibiting transport. Etidocaine is less potent than tetracaine at blocking transport since 2 mM etidocaine reduces the quantity 3H-proteins at a ligature by less than 10% and 2 mM tetracaine reduces it by greater than 90%. Etidocaine is, however, more potent than lidocaine since 10 mM etidocaine reduces the quantity of 3H-proteins present at a ligature by 64% and 10 mM lidocaine reduces it by less than 10%; when tested at the same pH (6.2) as the 10 mM etidocaine solution, 2 mM tetracaine reduces radioactivity at the ligature by 49%. The ratio of concentration required to block transport (by greater than 90%) to minimum anesthetic concentration is approximately 3 for tetracaine; but this ratio is much higher for etidocaine, since etidocaine is as potent as tetracaine as a local anesthetic but approximately 5 times less potent at inhibiting fast axonal transport.