The Toxins Act Intracellularly after Endocytosis

A recent report suggested that some kind of transmembrane signaling event, activating a calcium influx, occurs rapidly after ToxB contact with cells and is required for the disruption of actin filaments (Gilbert et al., 1995). However, a calcium influx is required for endocytosis of ToxB (Caspar et al., 1987), which may explain this observation. 

In conclusion, cellular internalization of the toxins is required for intoxication. This is consistent with the molecular mode of intracellular cytotoxic action of both toxins described below. 

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