Abstract

The stimulant drug amphetamine is postulated to enhance dopamine release through the plasmalemmal dopamine transporter by an exchange diffusion with synaptosomal dopamine. Because protein kinase C has been shown to have an effect on dopamine transporter activity, we examined the effect of protein kinase C inhibitors on endogenous dopamine release stimulated by amphetamine in perfused rat striatal slices. At concentrations of 1 μM, the selective protein kinase C inhibitors chelerythrine, Ro31–8220 and calphostin C nearly completely inhibited endogenous dopamine release elicited by 1 μM amphetamine. The inactive analog bisindoylmaleimide V had no effect. Extracellular Ca⁺⁺ was not required for the effect of the inhibitors. The importance of vesicular dopamine release was examined by determining inhibitor activity in reserpine-treated rats. Dopamine release elicited by 1 μM amphetamine was not significantly altered in reserpine-treated rats compared with control animals. Ro31–8220 at 1 μM completely blocked amphetamine-induced dopamine release in reserpine-treated rats. Activation of protein kinase C with 250 nM of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate increased dopamine release, and the release was not additive with 1 μM amphetamine. Both chelerythrine and Ro31–8220 at 1 μM increased [³H]dopamine uptake by 17% and 30%, respectively, whereas a brief exposure to 12-O-tetradecanoylphorbol 13-acetate slightly inhibited [³H]dopamine uptake. Our results suggest that amphetamine-mediated dopamine release through the plasmalemmal transporter is highly dependent on protein kinase C activity.