Postsynaptic effect of i.v. anaesthetic agents at the neuromuscular junction.

The effects of sodium thiopentone 19-757 mumol/litre, sodium pentobarbitone 25-806 mumol/litre, propanidid 74-1186 mumol/litre, Althesin 55-220 mumol/litre, diazepam 17.6-140 mumol/litre and ketamine 1.8-116.8 mumol/litre on the time-course of miniature end-plate currents of the excised mouse diaphragm were investigated. The currents were detected by means of extracellular electrodes and recorded with a transient recorder. The drugs had no significant effect on the growth phase of the current, but all six shortened the time-constant of the decay phase. This reduction in the duration of end-plate currents reduced the amplitude of postsynaptic potentials. A similar effect at central synapses may account for a failure of synaptic transmission caused by anaesthetic drugs and it is suggested that a reduction in the lifetime of open postsynaptic ionic channels is a common action of anaesthetic drugs.