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. [ 3 H]MPP + accumulation by CGNs exhibits first‐order kinetics, and a K t value of 5.3 ± 1.2 µ m and a T max of 0.32 ± 0.02 pmol per min per 10 6 cells. [ 3 H]MPP + accumulation is inhibited by corticosterone, β‐estradiol and decynium 22 with K i values of 0.25 µ m , 0.17 µ m and 4.0 n m respectively. [ 3 H]MPP + accumulation is also inhibited by desipramine, dopamine, serotonin and norepinephrine, but is not affected by carnitine (10 m m ), mazindol (9 µ m ) or GBR 12909 (1 µ m ). MPP + ‐induced caspase‐3‐like activation and cell death are prevented by pretreatment with 5 µ m β‐estradiol. In contrast, the neurotoxic effects of rotenone are unaffected by β‐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.