Use‐Dependent Conduction Block Produced by Volatile General Anesthetic Agents

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Abstract
The ability of a tertiary amine local anesthetic, barbiturates, and several volatile general anesthetics to block conduction of the compound action potential was measured in the frog sciatic nerve. Action potentials from large myelinated fibers were monitored using a desheathed nerve preparation in a sucrose‐gap chamber. Supramaximal stimuli were applied over a range of stimulus frequencies from 0.1 Hz to 500 Hz. All three anesthetic agents produced a phasic, frequency‐dependent anesthetic block, which developed with repetitive stimulation and returned to a tonic level when the nerve remained at rest. Saxitoxin produced a frequencyindependent block. The frequency‐dependent conduction blocks produced by the tertiary amine anesthetic and by the barbiturates were potentiated by elevated Ca2+in the solution bathing the nerve, but Ca2+changes did not modify the block produced by any of the volatile anesthetics, so the latter agents probably art by a diffrent mechanism than local anesthetics or barbiturates.