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Kent C. MacDougal, Matthew D. Johnson, and Karen G. Burnett

Marine Biomedical and Environmental Sciences, Department of Microbiology and Immunology, The Medical University of South Carolina, Charleston, SC 29412 USA

Abstract
Although fish in natural populations may carry high body burdens of both organic and inorganic mercury, the effects of this divalent metal on such lower vertebrates is poorly understood. In this report, inorganic mercury in the form of mercuric chloride (HgCl₂) is shown to produce both high-dose inhibition and low-dose activation of leukocytes in a marine teleost fish, Sciaenops ocellatus. Concentrations of inorganic mercury 10 M suppressed DNA synthesis and induced rapid influx of radiolabeled calcium, as well as tyrosine phosphorylation of numerous cellular proteins. Lower concentrations (0.1-1 M) of HgCl₂ that activated cell growth also induced a slow sustained rise in intracellular calcium in cells loaded with the calcium indicator dye fura-2, but did not produce detectable tyrosine phosphorylation of leukocyte proteins. These studies support the possibility that subtoxic doses of HgCl₂ may inappropriately activate teleost leukocytes, potentially altering the processes that regulate the magnitude and specificity of the fish immune response to environmental pathogens. Key words: calcium flux, cell signaling, leukocyte activation, mercury, tyrosine phosphorylation. Environ Health Perspect 104:1102-1106 (1996)