Effect of a sulfonium analog of dopamine on the depolarization-induced release of [ 3H]acetylcholine from mouse striatal slices

Abstract

We have synthesized a chemical analog or dopamine in which the amino group has been replaced by a charged dimethylsulfonium group. The dopaminergic activity of this drug was evaluated by determining its ability to inhibit the depolarization-evoked release of [ 3H]acetylcholine from mouse striatal slices. The slices were preincubated with [ 3H]choline (0.1 μM) and then superfused in physiological medium. [ 3H]Acetylcholine release was induced by exposure of the slices to a high potassium medium (12.5 mM) for 5 min. The sulfonium analog of dopamine, dopamine, and apormorphine inhibited the evoked [ 3H]acetylcholine release with IC 50 values of approximately 10, 2.0, and 0.3 μM respectively. The inhibition by the sulfonium analog was reversed by fluphenazine (1 μM), suggesting that the inhibition of [ 3H]acetylcholine release was due to the activation of dopaminergic receptors. The sulfonium analog also inhibited the uptake of [ 3H]dopamine into striatal slices and caused the release of exogenously taken up [ 3H]dopamine from these slices. The release of [ 3H]dopamine by the sulfonium analog was inhibited by cocaine (3 μM), suggesting that the drug-induced release of [ 3H]dopamine was dependent on the carrier-mediated uptake of the sulfonium analog into dopaminergic neurons. The inhibition of the evoked [ 3H]acetylcholine release by high concentrations (30 and 60 μM) of the sulfonium analog did not appear to be mediated by endogenous dopamine release, since the analog still inhibited [ 3H]acetylcholine release from slices after reserpine-α- methyl-p- tyrosine treatment, However, the inhibitory effect of the sulfonium analog at 10 μM was reduced by reserpine-α- methyl-p- tyrosine treatment, suggesting that the inhibition at lower concentrations was mediated through endogenous DA release. These results suggest that a charged compound can act as a substrate for the dopamine carrier and can activate the dopamine receptor regulating acetylcholine release. They also indicate that the nitrogen on the dopamine molecule is not essential for dopamine agonist activity.