Low-concentration lidocaine rapidly inhibits axonal transport in cultured mouse dorsal root ganglion neurons

Background: Axonal transport plays a critical role in supplying materials for a variety of neuronal functions such as morphogenetic plasticity, synaptic transmission, and cell survival. In the current study, the authors investigated the effects of the analgesic agent lidocaine on axonal transport in neurites of cultured mouse dorsal root ganglion neurons. In relation to their effects, the effects of lidocaine on the growth rate of the neurite were also examined. Methods: Isolated mouse dorsal root ganglion cells were cultured for 48 h until full growth of neurites. Video-enhanced microscopy was used to observe particles transported within neurites and to measure the neurite growth during control conditions and in the presence of lidocaine. Results: Application of 30 μM lidocaine immediately reduced the number of particles transported in anterograde and retrograde axonal directions. These effects were persistently observed during the application (26 min) and were reversed by lidocaine washout. The inhibitory effect was dose-dependent at concentrations from 0.1 to 1,000 μM (IC₅₀=10μM). In Ca²⁺-free extracellular medium, lidocaine failed to inhibit axonal transport. Calcium ionophore A23187 (0.1 μM) reduced axonal transport in both directions. The inhibitory effects of lidocaine and A23187 were abrogated by 10 μM KN-62, a Ca²⁺-calmodulin-dependent protein kinase II inhibitor. Application of such low-concentration lidocaine (30 μM) for 30 min reduced the growth rate of neurites, and this effect was also blocked by KN-62. Conclusions: Low-concentration lidocaine rapidly inhibits axonal transport and neurite growth via activation of calmodulin-dependent protein kinase II.