Inhibitory action of Ruthenium red on neuromuscular transmission

The effect of Ruthenium Red on synaptic transmission was examined at isolated junctions of the frog, by conventional methods for stimulation and intracellular recording. Ruthenium Red (2.5-10.0 muM) reduces the synaptic potential to subthreshold levels. An analysis of this phenomenon shows that the main action of Ruthenium Red is on the presynaptic nerve terminal where it decreases the number of quanta of transmitter liberated by the nerve impulse. It has the following additional effects: a reduction in the amplitude of the spontaneous miniature end plate potentials; an increase in their frequency; and an increase in delayed release of transmitter after a nerve impulse. Some of these results are discussed in terms of the known inhibitory action of Ruthenium Red on calcium transport across mitochondrial membranes.