Transmission in squid giant synapses: the importance of oxygen supply and the effects of drugs.

Synaptic transmission was studied in giant synapses of the stellate ganglion of the squid. When bathed in air-saturated sea water, the synapses deteriorate in 10 to 20 min.; if the sea water is saturated with 100 per cent oxygen, they function steadily for up to 12 hours. Optimal results probably require a medium with lower magnesium and higher calcium than the sea water used. Of eighteen compounds known to affect other synapses (Table I), none had stimulatory effects when applied to the preparation, but ten produced synaptic depression in concentrations of 10(-3) gm. per ml. or higher. The only exception was procaine, which blocked at 6 x 10(-5) gm. per ml. Intracellular recording with microelectrodes near the synapse showed that the block was associated with a slower rise of the excitatory post-synaptic potential, without a change in the depolarization required to initiate the spike. Procaine was exceptional in also increasing the depolarization at which the spike occurred.