[Regulation of tetanus toxin-inhibited transmitter secretion in the neuromuscular junction in a calcium-free medium]

The effect of Ca2+ removal from the external medium on regulation of the release of the synaptic transmitter in the tetanus toxin (TT)-inhibited neuromuscular junctions was studied on a rat phrenicodiaphragmal preparation with the aid of the conventional microelectrode technique of recording synaptic activity. As the external concentration of calcium was decreased from 2 to 0 mM, the frequency of miniature end plate potentials remained unchanged in the preparations isolated 3 to 3.5 h after intramuscular injection of TT (10(5) MLD for mouse). TT considerably reduced activation of the transmitter release, caused in intact synapses by ouabain (0.1 mM) and repetitive stimulation of the diaphragmatic nerve (50 imp/s). The data obtained indicate that in the TT-inhibited motor nerve terminals, the level of the transmitter release does not depend on the external concentration of calcium and that TT damages some of the intracellular sources of calcium.