Oxygen dependency of synaptic transmission at the squid Loligo pealei giant synapse.

1. Synaptic transmission at the squid giant synapse was blocked in 45 min by exposure to 0.02 atm oxygen but was maintained for more than 90 min in air (0.21 atm oxygen) or pure oxygen (1 atm). 2. Excitatory post-synaptic potential amplitude decreased in 0.02 atm oxygen but did not change in either 1 or 0.21 atm oxygen. Fast facilitation was increased in 0.02 atm oxygen only. 3. Post-synaptic resting membrane potential (Vm) and input resistance (Ro) remained unchanged in 1 or 0.21 atm oxygen but Ro was increased in 0.02 atm oxygen. 4. Our results suggest that severe hypoxia decreased the release of transmitter from the pre-synaptic terminal.