Opioid effects of racemic ketamine on the excitability of sciatic nerve and skeletal muscle fibers of the frog.

Abstract

The effects of +/- ketamine were tested on the excitability of frog sciatic nerves using a sucrose gap apparatus and skeletal muscle fibers using intracellular microelectrodes. When applied extracellularly by perfusion, ketamine depressed the action potential of sciatic nerves in a dose-dependent manner. This depression was partially antagonized by the simultaneous treatment with a small concentration of naloxone. However, when the ketamine was applied intracellularly by placing it in a compartment with a cut end of the nerve, only very small and inconsistent decreases were produced. Ketamine also blocked excitability in skeletal muscle by depressing the sodium conductance (gNa). This also could be partly antagonized by the addition of a small concentration of naloxone to the solution bathing the muscle. These results support previous findings by other workers that ketamine has a stereospecific opioid agonist effect in addition to its other actions.