Ca 2+ protects olfactory receptor function against acute Cu(II) toxicity in Atlantic salmon

Abstract

The effects of Ca 2+ and Mg 2+ on the acute toxicity of inorganic Cu(II) on the olfactory sense of Atlantic salmon ( Salmo salar L.) was studied by recording electro-olfactogram (EOG), the receptor potential, from the olfactory epithelium. In a series of experiments, the olfactory organ was irrigated with aqueous Cu(II) solutions containing Ca 2+ at concentrations ranging from 400 μM to 4000 μM. The effect of Mg 2+ was also tested by adding MgCl 2 (3600 μM Mg 2+) to the solution with lowest Ca 2+ concentration (400 μM). Stimulating the olfactory epithelium with L-alanine during Cu(II) exposure evoked atypical EOG responses. The amplitude and form of the EOG changed drastically with decreasing ionic strength of the solution. Both high Ca 2+ and high Mg 2+ concentration significantly reduced the immediate effects of Cu(II) exposure. Following a 5 min Cu(II) exposure, the EOG gradually recovered. After this recovery period (29 min) the EOG response was higher if a high concentration of Ca 2+ was included in the solutions. There was a significant correlation between the Ca 2+ concentration and the EOG response after recovery. By contrast, 3600 μM of Mg 2+ had no effect on the recovery. However, high Mg 2+ concentration reduced the immediate effects of Cu(II) exposure, probably by increasing the ionic strength of the solution and, thus, lowering Cu 2+ activity. In fact, a significant correlation was found between the calculated free Cu 2+ activity and the EOG response after 4 min of Cu(II) exposure.