The action of oxygen and oxygen at high pressure on inhibitory transmission

Abstract

The effect of 100% oxygen at ambient pressure, 100% oxygen at 1.7 Atmospheres Absolute (ATA), 100% oxygen at 5.1 ATA, helium at 1.7 ATA and helium at 5.1 ATA on inhibitory synaptic transmission was studied using the lobster walking leg neuromuscular preparation. Exposure to 100% oxygen at ambient pressure, at 1.7 ATA or at 5.1 ATA produced a decrease in inhibitoru transmission manifest as a fall in inhibitory synaptic conductance (G inh). The largest decrease in G inh was seen in 100% oxygen at ambient pressure. while a progressively smaller decrease was seen in 100% oxygen at 1.7 ATA and 5.1 ATA, respectively. Also associated with 100% oxygen at ambient pressure was the disappearance of inhibitory junction potentials. Pressurization with helium produced a fall in G inh at 5.1 ATA but no change or a slight increase at 1.7 ATA. The action of either 100% oxygen at ambient and at 1.7 or 5.1 ATA or helium at 1.7 or 5.1 ATA was shown to be on presynaptic parameters since the percent decrease in R o induced by oxogenous application of gamma-aminobutyric acid (GABA), the inhibitory transmitter, was the same in either 100% oxygen at ambient pressure, 100% oxygen or helium at 1.7 ATA and 5.1 ATA. The similarity in action of oxygen to the action of isoniazid, a known glutamic acid decar☐ylase (the enzyme that catalyzes the production of GABA) inhibitor in the same preparation suggests that one possible site of oxygen action is on GABA production.