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

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 Ca 2+ and Na + were measured by means of radiotracers and terminal blood samples were drawn for analysis of Ca 2+ and Na + . Plasma Ca 2+ was found not to be a reliable indicator of disturbances in branchial Ca 2+ fluxes. Cadmium specifically inhibited Ca 2+ influx, while having no effect on Ca 2+ efflux and only minor effects on Na + fluxes. The inhibition of Ca 2+ influx by Cd was modulated by water Ca 2+ content. Copper altered net Na + flux and plasma Na + in trout, while having only a transient effect on Ca 2+ homeostasis, the effects of Cu on the net Na + fluxes of trout were not modulated by either water Ca 2+ or pH. Hydrogen ion perturbed Ca 2+ dynamics predominantly by stimulating Ca 2+ 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.