Mechanism of action of pentobarbital on the contractile system of isolated frog muscle fibres.

The effects of pentobarbital-sodium were studied on single muscle fibres of frog skeletal muscle. In a concentration of 0.5 mM, pentobarbital potentiated the twitch response without significantly affecting the tetanus amplitude. The increase in twitch amplitude was accompanied by a marked increase in the rate of force development. The relaxation phase of both twitch and tetanus was prolonged. These mechanical changes were associated with an increased duration of the action potential. Pentobarbital also increased the amplitude and the rate of force development during the twitch after suppression by dantrolene. The S-shaped curve relating peak contracture tension and log caffeine concentration was shifted to the left by pentobarbital. It is suggested that pentobarbital affects the contractile activity of the muscle fibre; (1) by increasing the rate of release of calcium from its storage sites, (2) by prolonging the duration of the action potential and (3) by inhibiting calcium resequestration by the sarcoplasmic reticulum (SR).