Dantrolene effects on neuromuscular function in cat soleus muscle.

Dantrolene sodium (DS) was investigated for its effects on cat soleus muscle contractile properties and motor nerve terminal activity in particular. DS, 0.1-1.5 mg/kg i.v., caused a dose-dependent depression of indirectly elicited contractile strength which was more pronounced at lower frequencies of stimulation. Maximum tetanic strength at frequencies of 10-400 Hz was depressed to a lesser degree than contractile responses evoked by lower frequencies of stimulation; the twitch/tetanus contraction ratios were reduced with increasing dose, primarily because of diminished twitch. DS was without effect on motor nerve terminals as evidenced by normal post-tetanic repetition in the nerves following DS administration. Post-tetanic potentiation became relatively larger in amplitude as contractile strength was diminished. These data suggest that DS depresses neuromuscular function at a site other than the neural apparatus at the neuromuscular junction.