Dopamine transporter expression confers cytotoxicity to low doses of the parkinsonism-inducing neurotoxin 1-methyl-4-phenylpyridinium

Abstract

The uptake of 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of the parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was studied in various mammalian cell lines transfected, respectively, with the cloned human and rat dopamine transporters, and compared with rat striatal synaptosome preparations. Only in neuronally derived cell lines such as NG108-15, NS20Y, and SK-N-MC cells did MPP+ have a KM for the cloned transporters comparable to that of dopamine as seen in rat striatal synaptosomes. In non-neuronally derived cells such as COS-7, CHO, and Ltk- cells transiently or permanently expressing the transporters, the KM of MPP+ was at least 10-fold higher. The permanent expression of either the cloned human or rat dopamine transporters conferred to SK-N-MC cells susceptibility to the cytotoxic effects of low concentrations of MPP+. The extent of this effect was dependent on the expression level of the dopamine transporters and could be specifically antagonized by the catecholamine uptake inhibitor mazindol. There were no significant differences in the susceptibility to MPP+ of cells expressing similar levels of either the human or rat dopamine transporter. The demonstration for the first time of a quantitative relationship between the cellular expression of the plasma membrane transporter and the extent of the cytotoxic effects of MPP+ suggests that known differences in vulnerability of various brain regions to MPP+ cytotoxicity might be related to their actual content of dopamine uptake sites.(ABSTRACT TRUNCATED AT 250 WORDS)