1-Methyl-4-phenylpyridinium accumulates in cerebellar granule neurons via organic cation transporter 3

1-Methyl-4-phenylpyridinium (MPP+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, induces apoptosis in cerebellar granule neurons (CGNs). We have tested the hypothesis that organic cation transporter (OCT) 3 mediates the accumulation and, hence, the toxicity of MPP+ in CGNs. CGNs in primary culture express OCT3 but do not express mRNA for OCT1, OCT2 or the dopamine transporter. Cerebellar astrocytes are negative for OCT3 protein by immunocytochemistry. [H-3]MPP+ accumulation by CGNs exhibits first-order kinetics, and a K-t value of 5.3 +/- 1.2 mum and a T-max of 0.32 +/- 0.02 pmol per min per 10(6) cells. [H-3]MPP+ accumulation is inhibited by corticosterone, beta-estradiol and decynium 22 with K-i values of 0.25 mum, 0.17 mum and 4.0 nm respectively. [H-3]MPP+ accumulation is also inhibited by desipramine, dopamine, serotonin and norepinephrine, but is not affected by carnitine (10 mm), mazindol (9 mum) or GBR 12909 (1 mum). MPP+-induced caspase-3-like activation and cell death are prevented by pretreatment with 5 mumbeta-estradiol. In contrast, the neurotoxic effects of rotenone are unaffected by beta-estradiol. Interestingly, GBR 12909 protects CGNs from both MPP+ and rotenone toxicity. In summary, CGNs accumulate MPP+ in manner that is consistent with uptake via OCT3 and the presence of this protein in CGNs explains their sensitivity to MPP+ toxicity.