Anaesthetic and convulsant ethers act on different sites at the crab neuromuscular junction in vitro

Abstract

ATHOUGH volatile general anaesthetics, of the so called structurally non-specific type, have been shown to affect synaptic transmission^1,2, the underlying mechanisms are unknown. In view of their oil solubility, it has been suggested that these anaesthetics owe their depressant effect to the ability to induce non-specific disordering of membrane lipids^3,4. But some equally oil-soluble and structurally non-specific ethers are potent convulsants rather than anaesthetics⁵ and theoretical considerations suggest⁶ that the two groups act at different sites in the nervous system and therefore are more specific in action than assumed so far. In support of this, we now report that each of a pair of representative agents, methoxyflurane, an anaesthetic and hexafluorodiethylether (HFE, Indoklon, Ohio Medical and Surgical Suppliers), a convulsant, have different effects on excitatory or inhibitory transmission at the crab neuromuscular junction. We have found that in the adductor muscle of the crab, Ocypoda cursor, which contains both glutamate and γ–amino-butyrate (GABA) receptors, methoxyflurane blocks the action of glutamate but not of GABA, while HFE blocks the effect of GABA but not of glutamate.