Ketamine: effects on the mechanical properties of the frog sartorius muscle.

Isolated frog sartorius muscles were exposed to ketamine in concentrations up to 15 X 10(-5) M and the mechanical response to directly and indirectly stimulated muscles was studied. The effect on the directly elicited action potential was also investigated. The amplitude of the indirectly elicited twitches was decreased in a dose-dependent manner with a 50% decrease in twitch amplitude, at a ketamine concentration of 7.3 X 10(-5) M. The twitch amplitude was not affected by ketamine during direct stimulation of the muscle. However, direct tetanic stimulation of the muscle (80 Hz, 200 ms) revealed a decrease in the tetanic force of 20% during exposure to 7.3 X 10(-5) M ketamine. This decrease in tetanic force can be explained on the basis of effects on the sarcoplasmic reticulum, and/or the effects of ketamine on the directly elicited action potentials (decrease in amplitude and increase in duration) seen in these experiments. At concentrations of ketamine below about 4 X 10(-5) M, small effects were seen in this nerve-muscle preparation. If the effects on the frog muscle are similar to mammalian striated muscle, clinical concentrations of ketamine would have very small effects on the nerve-muscle system.