Uptake and Decarboxylation of l-3,4-Dihydroxyphenylalanine in Cultured Monkey Placenta Amniotic Epithelial Cells

In this study we tested the ability of monkey amniotic epithelial cells (MAEC) to take up and decarboxylate l-3,4-dihydroxyphenylalanine (l-DOPA) by incubating the cells in buffer containing l-DOPA under different experimental conditions followed by assaying cellular dopamine (DA) content using high performance liquid chromatography with electrochemical detection. Cellular contents of DA were significantly increased in a time- and l-DOPA-concentration-dependent manner, suggesting the uptake of l-DOPA by MAEC and indicating the presence of aromatic l-amino acid decarboxylase (AADC). This was confirmed by the decreased DA content in the presence of benserazide, an AADC inhibitor. Neither d-DOPA nor DA uptake blockers such as mazindol and GBR 12935 significantly affected l-DOPA uptake and hence DA levels. Further, synthesis of DA from l-DOPA was decreased in the presence of the amino acids tyrosine, phenylalanine and tryptophan, whereas the amino acids glycine and proline were without any significant effect. These findings suggest that MAEC have the capacity to selectively take up and decarboxylate l-DOPA with subsequent production of DA.