The Effects of Pentobarbital on the Electrical and Mechanical Properties of Frog and Snake Twitch Muscle Fibers

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Abstract
Pentobarbital (0.4–1.2 mM) produces marked enhancement of twitch tension in frog skeletal muscle. Latency is reduced and the rate of tension development is increased. In ordinary media, the agent impairs K contractures but this depressant effect can be eliminated by using a high calcium medium containing acetate in place of chloride. In such solutions, pentobarbital reduces the [K]0 necessary for K contractures. In snake twitch fibers depolarized by means of a voltage clamp, pentobarbital shifted the relation between membrane potential and contracture tension to a more negative level of potential. High concentrations of pentobarbital have a depolarizing effect which is greatly accentuated in a medium containing no permeant anion. The drug reduces the rate and extent of the depolarization produced by elevation of [K]0, and increases membrane resistance. These observations indicate that pentobarbital reduces the potassium permeability of the surface membrane of twitch muscle fibers.

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