Biochemical and pharmacological aspects of the synapses of the squid stellate ganglion

Abstract

The giant axon and isolated single giant synapses from the squid stellate ganglion were analyzed for acetylcholine (ACh), choline acetylase, and acetylcholinesterase (ACh-esterase). ACh, choline acetylase, and ACh-esterase are all present in significant quantities in the giant axon of the squid. Isolated single giant (distal) synapses from the squid stellate ganglion were found to have much higher concentrations of ACh, choline acetylase, and ACh-esterase than the giant axon. ACh and related compounds failed to affect the synapse when it was prepared in the usual way. Effects were seen, however, in carefully cleaned preparations from which surrounding connective tissue was removed; 5 × 10 −2 M ACh plus 10 −4 M physostigmine produced a reversible block of synaptic transmission in two of eight experiments, and an irreversible block was produced in the other six; 5 × 10 −2 M choline plus 10 −4 M physostigmine had no effect on the electrical activity of the synapse. The significance of the presence of the ACh system in the giant synapse and its structural and functional interrelationships are discussed.