Effect of a spider toxin (JSTX) on excitatory postsynaptic current at neuromuscular synapse of spiny lobster.

1. We studied the blocking properties of a spider (Nephila clavata) toxin (JSTX) purified from venom on the spiny lobster neuromuscular junction. 2. When a small amount of JSTX was applied to the neuromuscular junction, the excitatory postsynaptic potential (EPSP) was partially suppressed. The amplitude of EPSPs remained at a steady level for several hours during the washing of the preparation, showing that the action of JSTX is irreversible. 3. We recorded the excitatory postsynaptic current (EPSC) from synaptic site using a macro-patch electrode. The amplitude of EPSC increased linearly with hyperpolarization of the membrane potential in the presence and absence of JSTX. 4. The decay phase time constant of EPSC and spontaneous EPSC was decreased by hyperpolarizing the membrane potential both in the absence and in the presence of JSTX. The relationship between the decay time constant and the membrane potential was not modified by JSTX. 5. It is suggested that JSTX irreversibly blocks EPSC by acting on the site that is apart from the ionic channel of the glutamate receptor molecule.