The action of dantrolene on transmitter mobilization at the rat neuromuscular junction

Dantrolene sodium (20 microM) was found to decrease transmitter mobilization and the apparent available store of acetylcholine at frequencies of nerve stimulation of 50 and 100 Hz at the neuromuscular junction of the rat hemidiaphragm preparation treated with 2 microM (+)-tubocurarine. This effect of dantrolene sodium was not as marked at frequencies of nerve stimulation of 25 Hz or less, also no significant effect of the drug was observed on the amplitude of endplate potentials (EPPS) at any frequency of nerve stimulation. No effect of dantrolene sodium (20 microM) on mean miniature EPP amplitude or frequency was observed. It is suggested that the action of dantrolene sodium on mean EPP quantal content may be due to an action on stores of bound calcium within the motor nerve terminal. This effect of the drug is unlikely to be of physiological consequence in vivo, since it was only observed at high frequencies of nerve stimulation and did not cause a significant reduction of EPP amplitude during trains of stimuli.