Differential Regulation of Dopamine Transporter Function and Location
by Low Concentrations of Environmental Estrogens and 17β-Estradiol Rebecca A. Alyea and Cheryl S. Watson Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas, USA Abstract Background: The effects of 17β-estradiol (E2) and xenoestrogens (XEs) on dopamine transport may have important implications for the increased incidence of neurologic disorders, especially in women during life stages characterized by frequent hormonal fluctuations. Objective: We examined low concentrations of XEs [dieldrin, endosulfan, o´,p´‑dichlorodiphenylethylene (DDE) , nonylphenol (NP) , and bisphenol A (BPA) ] for nongenomic actions via action of membrane estrogen receptors (ERs) . Methods: We measured activity of the dopamine transporter (DAT) by the efflux of 3H-dopamine in nontransfected nerve growth factor–differentiated PC12 rat pheochromocytoma cells expressing membrane DAT, ER-α, ER-β, and G-protein–coupled receptor 30. We used a plate immunoassay to monitor trafficking of these proteins. Results: All compounds at 1 nM either caused efflux or inhibited efflux, or both ; each compound evoked a distinct oscillatory pattern. At optimal times for each effect, we examined different concentrations of XEs. All XEs were active at some concentration < 10 nM, and dose responses were all nonmonotonic. For example, 10–14 to 10–11 M DDE caused significant efflux inhibition, whereas NP and BPA enhanced or inhibited efflux at several concentrations. We also measured the effects of E2/XE combinations ; DDE potentiated E2-mediated dopamine efflux, whereas BPA inhibited it. In E2-induced efflux, 15% more ER-α trafficked to the membrane, whereas ER-β waned ; during BPA-induced efflux, 20% more DAT was trafficked to the plasma membrane. Conclusions: Low levels of environmental estrogen contaminants acting as endocrine disruptors via membrane ERs can alter dopamine efflux temporal patterning and the trafficking of DAT and membrane ERs, providing a cellular mechanism that could explain the disruption of physiologic neurotransmitter function. Key words: dopamine efflux, low concentrations, nongenomic, xenoestrogens. Environ Health Perspect 117:778–783 (2009) . doi:10.1289/ehp.0800026 available via http://dx.doi.org/ [Online 5 January 2009] Address correspondence to C.S. Watson, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0645 USA. Telephone/fax: (409) 772-2382. E-mail: cswatson@utmb.edu We thank D. Konkel for skillful editing of the manuscript. Financial support was provided by training grants from the National Institute of Environmental Health Sciences (T32 ES07254) and the National Institute on Drug Abuse (T32 DA07287) . The authors declare they have no competing financial interests. Received 21 July 2008 ; accepted 5 January 2009. The full version of this article is available for free in HTML or PDF formats. |