CA-2+ PROTECTS OLFACTORY RECEPTOR FUNCTION AGAINST ACUTE CU(II) TOXICITY IN ATLANTIC SALMON

The effects of Ca2+ and Mg2+ on the acute toxicity of inorganic Cu(II) on the olfactory sense of Atlantic salmon (Sabno 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 Ca2+ at concentrations ranging from 400 muM to 4000 muM. The effect of Mg2+ was also tested by adding MgCl2 (3600 muM Mg2+) to the solution with lowest Ca2+ concentration (400 muM). 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 Ca2+ and high Mg2+ 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 Ca2+ was included in the solutions. There was a significant correlation between the Ca2+ concentration and the EOG response after recovery. By contrast, 3600 muM of Mg2+ had no effect on the recovery. However, high Mg2+ concentration reduced the immediate effects of Cu(II) exposure, probably by increasing the ionic strength of the solution and, thus, lowering Cu2+ activity. In fact, a significant correlation was found between the calculated free Cu2+ activity and the EOG response after 4 min of Cu(II) exposure.