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Effects of inorganic mercury on [3H]dopamine release and calcium homeostasis in rat striatal synaptosomes. 1990

M F Hare, and S M Rezazadeh, and G P Cooper, and D J Minnema, and I A Michaelson
Department of Environmental Health, University of Cincinnati, College of Medicine, Ohio 45267-0056.

Inorganic mercury (Hg2+) in vitro increases spontaneous transmitter release from nerve terminals. The mechanisms of action are not well understood but may involve alterations in intraterminal Ca2+ dynamics. In this study we describe actions of Hg2+ in vitro on isolated mammalian CNS striatal nerve terminals (synaptosomes). Cobalt (2 mM) completely blocked the effect of 2 microM Hg2+ on spontaneous [3H]dopamine release. Cadmium (100 microM) was equipotent to Co2+ in blocking depolarization-dependent [3H]dopamine release, but did not alter the 2 microM Hg2(+)-induced spontaneous [3H]dopamine release. Depolarization-dependent [3H]dopamine release was not altered by 5 microM Hg2+. It appears that the site of action of Hg2+ on spontaneous [3H]dopamine release is not the Ca2+ channel. The effects of Hg2+ on intraterminal ionized Ca2+ [( Ca2+]i) were evaluated using the Ca2(+)-specific fluorescent probe, fura-2. Hg2+ (1-8 microM) had no effect on [Ca2+]i in 1.2 mM Ca2(+)-containing buffers. In nominal Ca2+ media, 4 and 8 microM Hg2+ significantly decreased [Ca2+]i. Following exposure to 4 and 8 microM Hg2+ the quenching of extrasynaptosomal fura-2 by Mn2+ was increased, suggesting that Hg2+ facilitated the leakage of fura-2. This apparent leakage was probably due to a nonspecific increase in membrane permeability since 2 microM Hg2+ produced a Co2(+)-insensitive increase in [3H]deoxyglucose phosphate efflux. Hg2+ did not increase the leakage of either lactate dehydrogenase or soluble protein from synaptosomes. Hg2+ produced a concentration-dependent (1-8 microM) increase in 45Ca2+ efflux from superfused synaptosomes which was insensitive to blockade either by 2 mM Co2+ or by 100 microM Cd2+. These data suggest that the transmitter releasing action of Hg2+ involves interactions with sites that also interact with Co2+ but not with Cd2+. Furthermore, Hg2+ may have direct transmitter releasing actions (i.e., Ca2(+)-mimetic properties), as well as nonspecific actions on plasma membrane permeability which may not necessarily be linked to [3H]dopamine release.

UI MeSH Term Description Entries
D007770 L-Lactate Dehydrogenase A tetrameric enzyme that, along with the coenzyme NAD+, catalyzes the interconversion of LACTATE and PYRUVATE. In vertebrates, genes for three different subunits (LDH-A, LDH-B and LDH-C) exist. Lactate Dehydrogenase,Dehydrogenase, L-Lactate,Dehydrogenase, Lactate,L Lactate Dehydrogenase
D008297 Male Males
D008564 Membrane Potentials The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization). Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D008628 Mercury A silver metallic element that exists as a liquid at room temperature. It has the atomic symbol Hg (from hydrargyrum, liquid silver), atomic number 80, and atomic weight 200.59. Mercury is used in many industrial applications and its salts have been employed therapeutically as purgatives, antisyphilitics, disinfectants, and astringents. It can be absorbed through the skin and mucous membranes which leads to MERCURY POISONING. Because of its toxicity, the clinical use of mercury and mercurials is diminishing.
D002104 Cadmium An element with atomic symbol Cd, atomic number 48, and atomic weight 112.41. It is a metal and ingestion will lead to CADMIUM POISONING.
D002118 Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D003035 Cobalt A trace element that is a component of vitamin B12. It has the atomic symbol Co, atomic number 27, and atomic weight 58.93. It is used in nuclear weapons, alloys, and pigments. Deficiency in animals leads to anemia; its excess in humans can lead to erythrocytosis. Cobalt-59,Cobalt 59
D003342 Corpus Striatum Striped GRAY MATTER and WHITE MATTER consisting of the NEOSTRIATUM and paleostriatum (GLOBUS PALLIDUS). It is located in front of and lateral to the THALAMUS in each cerebral hemisphere. The gray substance is made up of the CAUDATE NUCLEUS and the lentiform nucleus (the latter consisting of the GLOBUS PALLIDUS and PUTAMEN). The WHITE MATTER is the INTERNAL CAPSULE. Lenticular Nucleus,Lentiform Nucleus,Lentiform Nuclei,Nucleus Lentiformis,Lentiformis, Nucleus,Nuclei, Lentiform,Nucleus, Lenticular,Nucleus, Lentiform,Striatum, Corpus
D004298 Dopamine One of the catecholamine NEUROTRANSMITTERS in the brain. It is derived from TYROSINE and is the precursor to NOREPINEPHRINE and EPINEPHRINE. Dopamine is a major transmitter in the extrapyramidal system of the brain, and important in regulating movement. A family of receptors (RECEPTORS, DOPAMINE) mediate its action. Hydroxytyramine,3,4-Dihydroxyphenethylamine,4-(2-Aminoethyl)-1,2-benzenediol,Dopamine Hydrochloride,Intropin,3,4 Dihydroxyphenethylamine,Hydrochloride, Dopamine
D005456 Fluorescent Dyes Chemicals that emit light after excitation by light. The wave length of the emitted light is usually longer than that of the incident light. Fluorochromes are substances that cause fluorescence in other substances, i.e., dyes used to mark or label other compounds with fluorescent tags. Flourescent Agent,Fluorescent Dye,Fluorescent Probe,Fluorescent Probes,Fluorochrome,Fluorochromes,Fluorogenic Substrates,Fluorescence Agents,Fluorescent Agents,Fluorogenic Substrate,Agents, Fluorescence,Agents, Fluorescent,Dyes, Fluorescent,Probes, Fluorescent,Substrates, Fluorogenic

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