Characterization of both dopamine uptake systems in rat striatal slices by specific pharmacological tools

Abstract

Previous results have shown that modifications of dopamine (DA) high-affinity uptake 1 and those of DA low-affinity uptake 2 in rat striatal slices were different after autoxidation of this model and in the presence of antioxidants. The aim of this study was to determine whether these two DA uptake systems correspond to two different dopamine transporters or rather to a single one. A lesion into the substantia nigra of animals by injection of 6-hydroxydopamine, a neurotoxic substance of nigrostriatal dopaminergic neurons led to the suppression of both DA uptake systems. These two DA uptake systems were not modified when animals were treated by reserpine or tetrabenazine, which inhibit the vesicular monoamine transporter. Moreover, they were sodium- and temperature-dependent. Experiments with specific inhibitors showed that 1-[2-(diphenylmethoxy) ethyl]-4-(3-phenylpropyl)-piperazine dihydrochloride (GBR-12935) and (E)-N-(3-iodoprop-2-enyl)-2 β-carbomethoxy-3 β-(4′-tolyl) nortropane chloride (PE2I), two selective DA uptake inhibitors, were significantly more potent than fluoxetine and nisoxetine (selective serotonin and norepinephrine uptake inhibitors respectively) in both DA uptake systems. However, the concentrations of these products inhibiting low-affinity uptake 2 by 50% were much greater than those for high-affinity uptake 1. Our data indicate that both DA uptake systems are neuronal, independent of the vesicular monoamine transporter, active and specific for dopamine. Our results suggest that high-affinity uptake 1 and low-affinity uptake 2 correspond to the same dopamine transporter, but would be situated at different levels in the striatal slice model. Uptake 1 could take place at the periphery of the slice whereas uptake 2 in the depth of the slice.