Squid Giant Synapse - Electrophysiology

Electrophysiology

Many essential elements of how all chemical synapses function were first discovered by studying the squid giant synapse. Early electrophysiological studies demonstrated the chemical nature of transmission at this synapse by making simultaneous intracellular recording from the presynaptic and postsynaptic terminals in vitro (Theodore Holmes Bullock and Hagiwara (1957), Hagiwara and Ichiji Tasaki (1958), Takeuchi and Takeuchi (1962). Classical experiments later on demonstrated that, in the absence of action potentials, transmission could occur (Bloedel et al. (1966), Katz and Miledi (1967), Kusano et al. (1967). The calcium hypothesis for synaptic transmission was directly demonstrated in this synapse by showing that at the equilibrium potential for calcium (+60 mV, calcium does not enter the presynaptic terminal) no transmitter is released (Bernard Katz and R. Miledi 1967). Thus, calcium entry and not the change in the transmembrane electric field is responsible for voltage clamp studies that determined the relationship between the time course and amplitude of the calcium current and the amount of transmitter release directly determined (Llinas et al. 1981, Augustine et al. 1985) This preparation continues to be the most useful for the study of the molecular and cell biological basis for transmitter release. Other important new mammalian preparations are now available for such studies such as the calyx of Held.