Uptake of 1-methyl-4-phenylpyridinium (MPP+) by the JAR human placental choriocarcinoma cell line: comparison with 5-hydroxytryptamine.

The aim of this work was to characterize the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) in the JAR human choriocarcinoma cell line. As JAR cells, as well as the placenta, express the neuronal serotonin transporter (SERT), a comparison between the uptake of (3)H-MPP(+) and (3)H-serotonin ((3)H-5HT) was made. Specific uptake of (3)H-MPP(+) (0.2 microM ) was temperature-, Na(+)- and potential-dependent. 5HT and MPP(+) reduced (3)H-MPP(+) specific uptake (for 5HT, its IC(50) was found to be 4 microM ). The SERT inhibitors desipramine and fluoxetine also inhibited (3)H-MPP(+) specific uptake (with IC(50)s of 189 and 0.92 microM, respectively). The inhibitors of the extraneuronal monoamine transporter (EMT) and of the organic cation transporter type 2 (OCT2), corticosterone and decynium22, had no effect on (3)H-MPP(+) specific uptake, but cyanine863 concentration-dependently reduced it (with an IC(50) of 23 microM ). Specific uptake of (3)H-5HT (0.2 microM ) by JAR cells was temperature-, Na(+)- and potential-dependent. 5HT, MPP(+), desipramine and fluoxetine concentration-dependently inhibited (3)H-5HT specific uptake (with IC(50)s of 1.9 microM, 50 microM, 0.17 microM and 0.046 microM, respectively). Corticosterone showed no effect, but decynium22 and cyanine863 significantly reduced(3) H-5HT specific uptake. For cyanine863, its IC(50) was found to be 11 microM. In conclusion, the results suggest that: (1) uptake of (3)H-5HT by JAR cells occurs exclusively through SERT; (2) uptake of(3) H-MPP(+) by JAR cells involves SERT and also another transporter; (3) neither EMT nor OCT2 are functionally present in JAR cells.