BAFILOMYCIN A1 INHIBITS THE ACTION OF TETANUS TOXIN IN SPINAL-CORD NEURONS IN CELL-CULTURE

Tetanus toxin (TeNT) is one of the clostridial neurotoxins that act in tracellularly to block neurotransmitter release. However, neither the route of entry nor the mechanism by which these toxins gain access to the neuronal cytoplasm has been established definitively. In murine sp inal cord cell cultures, release of the neurotransmitter glycine is pa rticularly sensitive to blockade by TeNT. To test whether TeNT enters neurons through acidic endosomes or is routed through the Golgi appara tus, toxin action on potassium-evoked glycine release was assayed in c ultures pretreated with bafilomycin A1 (baf A1) or brefeldin A (BFA). baf A1, which inhibits the vacuolar-type H+-ATPase responsible for end osome acidification, diminishes the staining of acidic compartments an d interferes with the action of TeNT in a dose-dependent manner. TeNT blockade of evoked glycine release is inhibited by 50 and 90% in cultu res pretreated with 50 and 100 nM bat A1, respectively, compared with cultures treated with the inhibitor alone. The effects of baf A1 are f ully reversible. In contrast, BFA, which disrupts Golgi function, has no effect on TeNT action. These findings provide evidence that TeNT en ters the neuronal cytoplasm through bai A1-sensitive acidic compartmen ts and that TeNT is not trafficked through the Golgi apparatus before its translocation into the neuronal cytosol.