title: Effect of mercury on unidirectional sodium and calcium influx in Asellus aquaticus.
abstract: The effect of mercuric chloride (HgCl2) and monomethyl mercury chloride (CH3HgCl) on unidirectional 22Na and 45Ca influx were measured in the freshwater isopod Asellus aquaticus. Flux measurements involved short-term (20 min) exposure to 22Na or 45Ca following 2 h pre-exposure to Hg. Experiments were conducted at two different Na and Ca concentrations, 0.025 mmol L-1 and 0.25 mmol L-1. HgCl2 and CH3HgCl inhibited Na influx at both Na concentrations although Na influx at 0.25 mmol L-1 was always higher. This reflected the uptake kinetics of the Na pump which was determined to be saturable with a kmax values of 32 mumol Na g-1 h-1 and a Km value of 0.8 mmol L-1. CH3HgCl generally resulted in relatively greater inhibition of Na influx. At 0.025 mmol Na L-1 all CH3HgCl concentrations tested were inhibitory to Na influx, i.e., the lowest observed effect concentration (LOEC) was less than 0.04 mumol L-1. Ca influx was inhibited by HgCl2 at all concentrations tested (LOEC less than 0.04). The degree of inhibition was unaffected by Ca concentration, which was seen as evidence for non-competitive inhibition. However, CH3HgCl, which inhibited Ca influx from 0.025 mmol Ca L-1 by greater than 68% at molar Hg concentrations greater than or equal to 1 mumol L-1 showed no significant inhibitory affect at 0.25 mmol Ca L-1. Elimination of CH3HgCl inhibition at the higher Ca concentration suggests competition in this case, possibly at the level of access to the Ca pump.
authors.affiliation: University of Maryland System, Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, Solomons 20688-0038.
authors.forename: D A
authors.initials: DA
authors.lastname: Wright
authors.forename: P M
authors.initials: PM
authors.lastname: Welbourn
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003445:Crustacea / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008628:Mercury / Q000633:toxicity*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008628:Mercury; D002118:Calcium