Mercury is a pervasive occupational and environmental neurotoxicant of unknown cellular mechanism. A preliminary study by the P.I. showed that mercury in low concentration selectively inhibits glutamate uptake into primary cell cultures of mouse cerebral astrocytes. Glutamate and related endogenous neuroexcitants are themselves suspected of involvement in adult-onset primary neurodegenerative disorders. It is hypothesized that selective blockade of glutamate inactivation may be a contributory mechanism in mercury neurotoxicity. The proposed research will determine whether a cellular basis exists for this hypothesis.
The aim of the research is to explore the selective impairment of characterized amino acid transport systems by the toxic action of mercuric chloride and methylmercury(II) chloride. Anionic (Systems X-AG, X-A), neutral (Systems A, L, ASC, N, beta, GABA), and cationic (System y+) amino acid transport systems will be probed. This analysis will be correlated with cell mercury content and subcellular distribution, and with functional and morphologic status in mouse cerebral astrocytes. Radioactive tracers will be used to measure amino acid transport, leucine incorporation into protein, glucose utilization and mercury content of the astrocytes. Membrane integrity will be probed by vital dye exclusion and tracer efflux. Ultrastructural analysis of the cells and scanning X-ray microanalysis of mercury distribution will be carried out using quick-freeze fixation and cryopreparative techniques. A consultative and collaborative arrangement has been made for fluorometric assay of intermediates and metabolites of glycolytic and oxidative pathways. The proposed research will provide answers to fundamental questions concerning the cellular neurotoxic mechanism of mercury. These answers will be in a form that can be quantitatively, and therefore meaningfully, related to in vivo studies. The results will have a direct bearing upon (a) the need to provide a sound basis for defining tolerable tissue burdens of mercury in humans, (b) alternative therapeutic approaches in management of mercury intoxication, and (c) exploration of possible linkages between environmental neurotoxicants and primary neurodegenerative disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Research Project (R01)
Project #
1R01ES003928-01A1
Application #
3251658
Study Section
Toxicology Study Section (TOX)
Project Start
1986-06-15
Project End
1989-05-31
Budget Start
1986-06-15
Budget End
1987-05-31
Support Year
1
Fiscal Year
1986
Total Cost
Indirect Cost
Name
University of Maryland Baltimore
Department
Type
Schools of Medicine
DUNS #
003255213
City
Baltimore
State
MD
Country
United States
Zip Code
21201
Nagaraja, T N; Brookes, N (1998) Intracellular acidification induced by passive and active transport of ammonium ions in astrocytes. Am J Physiol 274:C883-91
Brookes, N (1997) Intracellular pH as a regulatory signal in astrocyte metabolism. Glia 21:64-73
Tsai, M J; Chang, Y F; Schwarcz, R et al. (1996) Characterization of L-alpha-aminoadipic acid transport in cultured rat astrocytes. Brain Res 741:166-73
Nagaraja, T N; Brookes, N (1996) Glutamine transport in mouse cerebral astrocytes. J Neurochem 66:1665-74
Nagaraja, T N; Brookes, N (1996) Mercuric chloride uncouples glutamate uptake from the countertransport of hydroxyl equivalents. Am J Physiol 271:C1487-93
Judd, M G; Nagaraja, T N; Brookes, N (1996) Potassium-induced stimulation of glutamate uptake in mouse cerebral astrocytes: the role of intracellular pH. J Neurochem 66:169-76
Brookes, N; Turner, R J (1994) K(+)-induced alkalinization in mouse cerebral astrocytes mediated by reversal of electrogenic Na(+)-HCO3- cotransport. Am J Physiol 267:C1633-40
Brookes, N (1993) Interaction between the glutamine cycle and the uptake of large neutral amino acids in astrocytes. J Neurochem 60:1923-8
Brookes, N; Turner, R J (1993) Extracellular potassium regulates the glutamine content of astrocytes: mediation by intracellular pH. Neurosci Lett 160:73-6
Brookes, N (1992) Regulation of the glutamine content of astrocytes by cAMP and hydrocortisone: effect of pH. Neurosci Lett 147:139-42

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