[Effect of methylene blue on spontaneous and evoked reactions in the autonomic neuromuscular junction]

The action of a vital neurotropic dye methylene blue on spontaneous and posttetanic reactions in the autonomic neuromuscular junction was studied with the sucrose gap technique. Low concentrations of methylene blue (10(-5)-10(-6) g/ml) increased the frequency of APs in spontaneously active cells and induced APs in silent cells while high concentrations of methylene blue (10(-3)-10(-4) g/ml) showed the biphasic excitatory-inhibitory action. Similar changes occurred in the excitatory phase of posttetanic response of smooth muscle cells, although the amplitude and duration of synaptic potentials remained unchanged. The stability of reactions after injection of methylene blue simultaneously with ganglio-, adrenoblocking agents and atropine as well as elevated Mg2+, suggests unspecific action of the methylene blue molecule on the muscle cell membrane. The observed phenomena were of shortlasting type and disappeared after washing with normal nutrient medium.