Enhancement of skeletal muscle fatigue by the calcium channel antagonist diltiazem.

This study sought to determine the effects of diltiazem on normal muscle twitches and on twitches evoked during repetitive stimulation. Initial experiments showed that diltiazem (5 and 30 microM) had slight, but insignificant, effects on peak twitch tension and the time course of the twitch. When muscles were stimulated at 1 or 5 Hz, 30 microM diltiazem significantly depressed the height and time course of the staircase period and increased the rate and magnitude of fatigue. Contrary to control, diltiazem caused a complete loss of developed tension during both stimulation protocols. Results suggest that although diltiazem has little effect on single twitches, it has marked inhibitory effects on twitches evoked during repetitive activity; the result being enhancement of the fatigue process.