Fast and slow skeletal muscles: effect of secobarbital on contractility of muscles from mice.

In vitro studies were performed on fast and slow muscles from mice to determine if secobarbital sodium (SCB) has a direct effect on muscle contractility. All preparations were curarized and stimulation was direct. After baseline studies, SCB was added to the muscle bath in 1 of 4 concentrations-10, 20, 100 and 200 microgram/ml. Tetanic tension was reduced for both muscle types at SCB concentrations greater than or equal to 20 microgram/ml, and loss was progressive with increasing dose. In contrast, twitch tension (P) was increased by SCB at the 2 higher concentrations. The increase in P was due to an increase in rate of tension development plus prolongation of the time parameter (duration) of the twitch. Fatigue was accelerated by SCB for both muscle types. The results indicate that SCB has a direct and similar effect on fast and slow skeletal muscles. The probable sites of action of the drug are the excitation contraction coupling mechanisms and the mechanisms for energy production and/or utilization.