Different effects of botulinum A toxin and tetanus toxin on the transmitter releasing process at the mammalian neuromuscular junction.

The quantal transmitter release of tetanus (TeTx) and botulinum A (BoTx) toxin paralyzed mouse diaphragms was studied. The very low release probability could be enhanced by increasing the frequency of nerve stimulation to 50 Hz or by the application of 4-aminopyridine. In the BoTx-muscles the endplate potentials were strongly coupled to the stimuli with synaptic delays similar to unpoisoned terminals. In contrast, in the TeTx-muscles large variations in the delay of release of quanta in response to stimulation were observed. From these findings it is suggested that TeTx and BoTx act at different sites of the depolarization-transmitter release process.