Batrachotoxin blocks saltatory organelle movement in electrically excitable neuroblastoma cells

Batrachotoxin has been reported to inhibit fast axonal transport. We have examined the effect of batrachotoxin on saltatory organelle movements in N115 neuroblastoma cells (a model of fast axonal transport) using time-lapse video intensification microscopy. Batrachotoxin (0.1–1.0 μM) inhibits saltatory organelle movement. Contrary to previously published hypotheses, this inhibition of intra-axonal movement depends upon the action of batrachotoxin on action potential Na⁺ channels. Evidence for this conclusion is: (1) the range of concentrations of batrachotoxin which inhibit saltatory organelle movement is consistent with the dose-response curve for the activation of action potential Na⁺ channels by batrachotoxin in N18 neuroblastoma cells¹⁰; (2) tetrodotoxin, which blocks action potential Na⁺ channels, prevents the inhibition of organelle movements by batrachotoxin; (3) batrachotoxin has no effect on saltatory movement in cells, including some neuroblastoma cell lines, which lack action potential Na⁺ channels; and (4) in Na⁺-free or low Na⁺ media, batrachotoxin does not block organelle movement. We suggest that changes in internal ion concentrations which follow the influx of Na⁺ are responsible for the inhibition of fast axonal transport by batrachotoxin.