Preliminary results of parts of this study were presented at the 19th Annual Meeting of the Society for Neuroscience and the 33rd Annual Meeting of the Society of Toxicology and were published in abstract form in Soc. Neurosci. Abstr. (1993) 19, 1749, and The Toxicologist (1994) 14, 290. This work was submitted by M.F.D. in partial completion of the requirements of the Ph.D. degree in Pharmacology and Toxicology and Environmental Toxicology at Michigan State University.
Methylmercury-Induced Elevations in Intrasynaptosomal Zinc Concentrations: An 19F-NMR Study†
Version of Record online: 23 NOV 2002
Journal of Neurochemistry
Volume 63, Issue 1, pages 383–386, July 1994
How to Cite
Denny, M. F. and Atchison, W. D. (1994), Methylmercury-Induced Elevations in Intrasynaptosomal Zinc Concentrations: An 19F-NMR Study. Journal of Neurochemistry, 63: 383–386. doi: 10.1046/j.1471-4159.1994.63010383.x
- Issue online: 23 NOV 2002
- Version of Record online: 23 NOV 2002
- Resubmitted manuscript received April 5, 1994; accepted April 11, 1994.
- Heavy metal
Abstract: Methylmercury (MeHg) increases the concentration of intracellular Ca2+ ([Ca2+]i) and another endogenous polyvalent cation in both synaptosomes and NG108-15 cells. In synaptosomes, the elevation in [Ca2+]i was strictly dependent on extracellular Ca2+ (Ca2+e); similarly, in NG108-15 cells, a component of the elevations in [Ca2+]i was Ca2+e dependent. The MeHg-induced elevations in endogenous polyvalent cation concentration were independent of Ca2+e in synaptosomes and NG108-15 cells. The pattern of alterations in fura-2 fluorescence suggested the endogenous polyvalent cation may be Zn2+. Using 19F-NMR spectroscopy of rat cortical synaptosomes loaded with the fluorinated chelator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N′,N′-tetraacetic acid (5F-BAPTA), we have determined unambiguously that MeHg increases the free intrasynaptosomal Zn2+ concentration ([Zn2+]i). In buffer containing 200 µM EGTA to prevent the Ca2+e-dependent elevations in [Ca2+]i, the [Zn2+]i was 1.37 ± 0.20 nM; following a 40-min exposure to MeHg-free buffer [Zn2+]i was 1.88 ± 0.53 nM. Treatment of synaptosomes for 40 min with 125 µM MeHg yielded [Zn2+]i of 2.69 ± 0.55 nM, whereas 250 µM MeHg significantly elevated [Zn2+]i to 3.99 ± 0.68 nM. No Zn2+ peak was observed in synaptosomes treated with the cell-permeant heavy metal chelator N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN, 100 µM) following 250 µM MeHg exposure. [Ca2+]i in buffer containing 200 µM EGTA was 338 ± 26 nM and was 370 ± 64 nM following an additional 40-min exposure to MeHg-free buffer. [Ca2+]i was 498 ± 28 or 492 ± 53 nM during a 40-min exposure to 125 or 250 µM MeHg, respectively. None of the values of [Ca2+]i differed significantly from either pretreatment levels or buffer-treated controls.