The role of de novo catecholamine synthesis in mediating methylmercury-induced vesicular dopamine release from rat pheochromocytoma (PC12) cells

Abstract

The purpose of this study was to characterize methylmercury (MeHg)-induced dopamine (DA) release from undifferentiated pheochromocytoma (PC12) cells and to examine the potential role for DA synthesis in this process. MeHg caused a significant increase in DA release that was both concentration- and time-dependent. DA release was significantly increased by 2μM MeHg at 60min and by 5μM MeHg at 30min; 1μM MeHg was without effect. Because DA release induced by 5μM MeHg was associated with a significant percentage of cell death at 60 and 120min, 2μM MeHg was chosen for further characterization of release mechanisms. MeHg-induced DA release was attenuated but not abolished in the absence of extracellular calcium, whereas the vesicular content depleting drug reserpine (50nM) abolished release. Thus, MeHg-induced DA release requires vesicular exocytosis but not extracellular calcium. MeHg also increased intracellular DA and the rate of DA storage utilization, suggesting a role for DA synthesis in MeHg-induced DA release. The tyrosine hydroxylase inhibitor α-methyltyrosine (300μM, 24h) completely abolished MeHg-induced DA release. MeHg significantly increased DA precursor accumulation in cells treated with 3-hydroxybenzylhydrazine (10μM), revealing that MeHg increases tyrosine hydroxylase activity. Overall, these data demonstrate that MeHg facilitates DA synthesis, increases intracellular DA, and augments vesicular exocytosis. © The Author 2013. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.