Effects of Cadmium, Copper, and Low pH on Ion Fluxes in the Rainbow Trout,Salmo gairdneri

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Abstract
Adult and juvenile rainbow trout, Salmo gairdneri, acclimated to high and low water Ca levels were statically exposed to equimolor concentrations (~ 6.5 μmolùL−1) of Cd or Cu at circumneutral pH or pH 4.8 either alone or in metal/H+combinations for 24 h. Unidirectional fluxes of Ca2+and Na+were measured by means of radiotracers and terminal blood samples were drawn for analysis of Ca2+and Na+. Plasma Ca2+was found not to be a reliable indicator of disturbances in branchial Ca2+fluxes. Cadmium specifically inhibited Ca2+influx, while having no effect on Ca2+efflux and only minor effects on Na+fluxes. The inhibition of Ca2+influx by Cd was modulated by water Ca2+content. Copper altered net Na+flux and plasma Na+in trout, while having only a transient effect on Ca2+homeostasis, the effects of Cu on the net Na+fluxes of trout were not modulated by either water Ca2+or pH. Hydrogen ion perturbed Ca2+dynamics predominantly by stimulating Ca2+efflux, while reducing influx only slightly. Exposure to elevated H+(pH 4.8) had no significant effect on net Na+balance over the 24-h period. These data indicate significant differences in the toxic mechanisms of three metals with similar ligand binding chemistry.
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