Methylmercury transport

Kerper LE, Ballatori N, Clarkson TW. 1992. Methylmercury transport across the blood-brain barrier by an amino acid carrier. Am J Physiol 262 R761-R765. 

Mason, R.P. Sullivan, K.A. 1998. Mercury and methylmercury transport through an urban watershed. Water Research, 32, 321-330... 

Methylmercury transport between all compartments except brain and hair is modeled as plasma flow limited (i.e., plasma levels rapidly equilibrate with erythrocytes). Mercuric mercury transport parameters... 

The compartments and barriers to methylmercury transport in the tissue compartments and placenta are shown in Figure 2-6. The cell membrane is assumed to be the barrier for methylmercury transport for all tissues except the brain and placenta. The barrier to methylmercury transport to the brain is the endothelial cell wall of the cerebral vascular system (the blood-brain barrier). The placenta is modeled as four compartments, with separate transfer constants for placental barrier and placental tissue transport. There is a tissue compartment for both the maternal and fetal sides of the placenta. 

Ballatori, N University of Rochester Rochester, NY Methylmercury transport across cell membranes. NIEHS... 

Methylmercury transport across the blood-brain barrier appears to be mediated by the large neutral amino acid transport system (system L) on the luminal surface of brain capillary endothelial cells (Kerper et al. 1992). Previous in vivo studies had shown that the amino acid, L-cysteine, accelerates methylmercury uptake into brain in vivo, but the mechanism was not identified. Because the methylmercury-L-cysteine complex has close struc-... 

Kerper LE, Ballatori N, Clarkson TW (1992) Methylmercury transport across the blood-brain barrier by an amino acid carrier. Am J Physiol 262 R761-R765 Kinter WB, Pritchard JB (1977) Altered permeability of cell membranes. In DHK See (ed) Handbook of physiology—reactions to environmental agents. American Physiol Society, Baltimore, MD, pp 563-576 Knauf PA, Rothstein A (1971) Effects of sulfhydryl and amino reactive reagents on anion and cation permeability of the human red blood cell. J Gen Physiol 58 190-210... 

Babiarz CL, Hurley JP, Benoit JM, Shafer MM, Andren AW, Webb DA. 1998. Seasonal influences on partitioning and transport of total and methylmercury in rivers from contrasting watersheds. Biogeochemistry 41 237-257. 

Aschner M, Yao CP, Allen JW, Tan KH. 2000. Methylmercury alters glutamate transport in astrocytes. Neurochem Int 37 199-206. 

Long-range atmospheric transport of Hg from fossil fuel combustion and solid waste incineration has increased Hg in freshwater and biota. In the United States, combustion of fossil fuels for power generation is estimated to generate about 30% of the total release of Hg into the atmosphere (Harriss and Hohenemser, 1978). One in every three lakes in the United States and nearly one-quarter of the nation s rivers contain various pollutants, including Hg (CNN, 2004). Forty States in the U.S. have issued advisories for methylmercury on selected water-bodies, and 13 states have statewide advisories for some or all sportfish from rivers or lakes (USGS, 2000). Fish consumption advisories for methylmercury account for more than three-quarters of all fish consumption advisories. 

Simmons-Willis, T. A., et al. Transport of a neurotoxicant by molecular mimicry the methylmercury-l-cysteine complex is a substrate for human L-type large neutral amino acid transporter (LAT) 1 and LAT2. Biochem. J. 2002, 367, 239-246. 

Other Mechanisms. We acknowledge that numerous other processes (such as detritivore activity and microbial transformations) may affect transport across the interface, but our techniques could evaluate only the processes previously discussed. An obvious area for future research is microbial degradation and release of methylmercury from sediments. The assessment of factors regulating this transformation and release is essential for predictive models on Hg transport and bioaccumulation. 

Lawson, N.M., R.P. Mason, and J.-M. Laporte. 2001. The fate and transport of mercury, methylmercury, and other trace metals in Chesapeake Bay tributaries. Water Res. 35 501-515. 

Shanker, G., and Aschner, M. (2001). Identification and characterization of uptake systems for cystine and cysteine in cultured astrocytes and neurons Evidence for methylmercury-targeted disruption of astrocyte transport. J. Neurosci. Res. 66, 998-1002. 

Finally, lipid-soluble chemicals like the insecticide DDT, polychlorinated biphenyls, and methylmercury are excreted readily as dissolved chemicals into milk fat droplets. Lead is secreted into milk using the same transport system as calcium. Nursing mothers may therefore transfer environmental contaminants to their infants - not to the point, however, of negating the well-established benefits of breastfeeding. 

Thiomerosal is metabolized to ethylmercury and thiosalicylate. Toxicologists have assumed that ethylmercury poisoning is similar to the toxicity of me-thylmercury. Flowever, ethylmercury cannot bypass the blood-brain barrier as easily as methylmercury. The entry of methylmercury into the brain relies on an active transport system. Ethylmercury on the other hand is a larger molecule and cannot use this system. Furthermore, it is more rapidly decomposed. Because of these limitations, when the same dose of both mercurial compounds is administered, the concentrations of methylmercury are greater in the brain when compared to ethylmercury. Due to the limited entry of the latter into the brain, this compound is more likely to cause damage to the spinal cord, myocardium and skeletal muscle. 

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