Abstract

The food dye erythrosin B has been reported to inhibit the neuronal uptake of catecholamines. To test this hypothesis we examined the effect of the dye on the responses of neurons in amphibian sympathetic ganglia to both dopamine and epinephrine. Although the hyperpolarizations induced by both catecholamines were potentiated by the conventional uptake blocker, desipramine (0.5 microM), low doses of erythrosin B (1-10 microM) produced an irreversible blockade. It was therefore not possible to evaluate the hypothesis that the dye might block catecholamine uptake. Xanthine dyes such as erythrosin B have also been reported to inhibit Na-K-adenosine triphosphatase. In agreement with this possibility we found that erythrosin B promoted irreversible inhibition of the (nicotinic) acetylcholine after-hyperpolarization. This response is generated by the electrogenic activity of the Na+ pump. Neither this Na+ pump inhibition nor erythrosin-induced membrane hyperpolarization appeared to account for the effect of the dye on catecholamine responses. The irreversible antagonism of epinephrine and dopamine by erythrosin was specific in that hyperpolarizing responses to muscarinic antagonists such as methacholine were relatively insensitive to the dye. It is therefore concluded that erythrosin B selectively antagonizes responses to catecholamines in amphibian sympathetic ganglia. No information as to the exact molecular mechanism of this antagonism is available from the present experiments.