Blockade of synaptic transmission in the squid giant synapse by a spider toxin (JSTX).

We studied the effect of spider toxin (JSTX)--specific blocker of glutamate receptor--on giant synapse of the squid stellate ganglion. JSTX irreversibly blocked the excitatory postsynaptic potential (EPSP) without affecting the presynaptic action potential or the antidromic action potential. L-glutamate depolarized the postsynaptic membrane and suppressed EPSP which may be due to desensitization. The action of glutamate was completely blocked in the presence of JSTX. The results suggest that glutamate is the transmitter at the giant synapse of squid.