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

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.