Tetanus antitoxin binds to intracellular tetanus toxin in permeabilized chromaffin cells without restoring Ca2(+)-induced exocytosis

Tetanus toxin blocks Ca2(+)-evoked catecholamine release from permeabilized bovine adrenal chromaffin cells preloaded with gangliosides. Tetanus toxin preincubated with its specific antibodies F(ab')2 is without any effect on exocytosis. Specific antitetanus F(ab')2 presented to chromaffin cells which are pretreated with tetanus toxin and permeabilized by digitonin cannot restore exocytosis. Under the same conditions, however, 125I-labeled F(ab')2 accumulates in chromaffin cells. The accumulation depends on the presence and concentration of tetanus toxin and can be prevented by an excess of unlabeled F(ab')2. Once tetanus toxin has initiated block of exocytosis, it cannot be neutralized by binding to its specific antibody.