THE NATURE OF GENTAMICIN-INDUCED NEUROMUSCULAR BLOCK

Gentamicin in concentrations of 0.05–0.2 mmol litre^–1blocked neuromuscular transmission in the toad sartorius nerve-musclepreparation by decreasing the release of transmitter. In concentrationsof 0.5–1 mmol litre^–1 it decreased the amplitudeof the miniature end-plate current by a curare-like action,without affecting the mean open channel lifetime. Present address: Division of Anaesthesia and Intensive Care,Prince Henry Hospital, Little Bay, N.S.W. 2036, Australia     

PRESYNAPTIC EFFECT OF I.V. ANAESTHETIC AGENTS AT THE NEUROMUSCULAR JUNCTION

The effect of Althesin, diazepam, ketamine, propanidid and thiopentoneon the release of acetylcholine was tested at the mouse neuromuscularjunction. Althesin, diazepam and thiopentone increased the quantalcontent of the end-plate potential. Ketamine at low concentration(3·6 (µmol litre^–11) had a similar effect,but at high concentration (116·7 µmol litre^–1)quantal content decreased sharply. Propanidid and cremophorEL did not affect quantal content. The increase in quantal contentantagonized the effect of postsynaptic depression on the amplitudeof the end-plate potential. The lack of enhancement of acetylcholinerelease appears to explain the in vitro interaction of propanididwith tubocurarine. The diversity of presynaptic actions of thesedrugs makes it unlikely that this is an important mechanismin producing anaesthesia.     

MYONEURAL ACTIONS OF ORG NC 45

In the toad sartorius preparation Org NC 45 reduced the meanquanta] content of the end-plate potential both in magnesiumand tubocuraine-treated preparations, as well as blocking post-junctionalreceptors. In a concentration which permits recording of theminiature end-plate current no channel block was demonstrated.