Potentiation and inhibition of ganglionic transmission by ruthenium red

The effect of ruthenium red, 2.5 to 5 muM, on ganglionic transmission in rat superior cervical ganglia and frog abdominal ganglia were studied in vitro. In rat ganglia, ruthenium red caused a spontaneous firing of ganglia cells, and an increase in the amplitude and duration of the compound action potential following a single stimulus volley. However, transmission following a conditioning volley or a repetitive stimulus train to the preganglionic nerve was depressed up to 60 sec. The asynchronous firing caused by bethanechol was potentiated by ruthenium red. In the frog, ruthenium red caused repetitive firing of ganglion neurons following either orthodromic or antidromic stimulation. It is suggested that the potentiation of the single potential and the spontaneous firing are due to a ruthenium red-induced increase in intracellular calcium concentration. The depression of transmission may be due to a temporary depletion of readily releasable acetylcholine. It is also suggested that ruthenium red has an effect on the postsynaptic membrane.