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Methylmercury‐Induced Elevations in Intrasynaptosomal Zinc Concentrations: An 19 F‐NMR Study
Author(s) -
Denny Michael F.,
Atchison William D.
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.63010383.x
Subject(s) - chemistry , egta , synaptosome , chelation , bapta , extracellular , fura 2 , calcium , methylmercury , intracellular , analytical chemistry (journal) , biophysics , nuclear chemistry , biochemistry , inorganic chemistry , chromatography , enzyme , organic chemistry , selenium , cytosol , biology
Methylmercury (MeHg) increases the concentration of intracellular Ca 2+ ([Ca 2+ ] i ) and another endogenous polyvalent cation in both synaptosomes and NG108‐15 cells. In synaptosomes, the elevation in [Ca 2+ ] i was strictly dependent on extracellular Ca 2+ (Ca 2+ e ); similarly, in NG108‐15 cells, a component of the elevations in [Ca 2+ ] i was Ca 2+ e dependent. The MeHg‐induced elevations in endogenous polyvalent cation concentration were independent of Ca 2+ e in synaptosomes and NG108‐15 cells. The pattern of alterations in fura‐2 fluorescence suggested the endogenous polyvalent cation may be Zn 2+ . Using 19 F‐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 Zn 2+ concentration ([Zn 2+ ] i ). In buffer containing 200 µ M EGTA to prevent the Ca 2+ e ‐dependent elevations in [Ca 2+ ] i , the [Zn 2+ ] i was 1.37 ± 0.20 n M ; following a 40‐min exposure to MeHg‐free buffer [Zn 2+ ] i was 1.88 ± 0.53 n M . Treatment of synaptosomes for 40 min with 125 µ M MeHg yielded [Zn 2+ ] i of 2.69 ± 0.55 n M , whereas 250 µ M MeHg significantly elevated [Zn 2+ ] i to 3.99 ± 0.68 n M . No Zn 2+ peak was observed in synaptosomes treated with the cell‐permeant heavy metal chelator N,N,N′,N′ ‐tetrakis(2‐pyridylmethyl)ethylenediamine (TPEN, 100 µ M ) following 250 µ M MeHg exposure. [Ca 2+ ] i in buffer containing 200 µ M EGTA was 338 ± 26 n M and was 370 ± 64 n M following an additional 40‐min exposure to MeHg‐free buffer. [Ca 2+ ] i was 498 ± 28 or 492 ± 53 n M during a 40‐min exposure to 125 or 250 µ M MeHg, respectively. None of the values of [Ca 2+ ] i differed significantly from either pretreatment levels or buffer‐treated controls.