N-n-Alkylnicotinium and N-n-Alkylpyridinium Analogs Inhibit the Dopamine Transporter: Selectivity as Nicotinic Receptor Antagonists

N-n-Alkylnicotinium and N-n-alkylpyridinium analogs act as antagonists at nicotinic acetylcholine receptors (nAChRs) mediating nicotine-evoked [ ³H]dopamine (DA) overflow from superfused rat striatal slices in the presence of a DA transporter (DAT) inhibitor. However, the potential interaction of these nAChR antagonists with DAT has not been evaluated. In the present study, analog inhibition of [³H]DA uptake into striatal synaptosomes and inhibition of [³H]GBR 12935 binding to striatal membranes was determined. N-n-Alkylnicotinium analogs with n-alkyl chains of C_6-12 and N-n-alkylpyridinium analogs with n-alkyl chains of C _7-20 inhibited [³H]DA uptake with a wide affinity range. With the exception of the C₂₀ N-n-alkylpyridinium, a linear relationship between chain length and inhibition of [³H]DA uptake was found in both analog series. Similarly, these analogs inhibited [ ³H]GBR 12935 binding (K_i=5.7-250 μM), and a linear relationship with chain length was observed, with the exception of the C ₈ N-n-alkylnicotinium analog. Kinetic analyses of inhibition of [³H]DA uptake and [³H]GBR 12935 binding using representative C₁₂ analogs from each series revealed decreases in maximal [³H]DA transport velocity and maximal [³H]GBR 12935 binding without alterations in affinity, indicating noncompetitive interactions with DAT. In comparison, classical nAChR antagonists (mecamylamine, dihydro-β-erythroidine and methyllycaconitine) did not inhibit [ ³H]DA uptake or [³H]GBR 12935 binding. Moreover, inhibition of DAT function occurred at analog concentrations 10-120-fold higher than those inhibiting nAChR function. Taken together with the inability of these analogs to inhibit field-stimulation-evoked [³H]DA overflow, the results indicate that these analogs act selectively as antagonists at nAChRs mediating nicotine-evoked [³H]DA overflow.