Copper binding dynamics and olfactory impairment in fathead minnows (Pimephales promelas)

When fish are exposed to sublethal, environmentally relevant Cu concentrations, olfactory acuity is impaired. The goals of the present study were to investigate the binding dynamics of waterborne Cu in the olfactory epithelium (OE), to examine the influence of calcium (Ca²⁺) on Cu binding, and to link Cu-OE binding to changes in olfactory acuity. Using short-term in vivo waterborne exposures to ⁶⁴Cu, we found that Cu accumulates rapidly in the OE, reaching a plateau by 3 h. The binding affinity (log K_Cu-OE) and binding capacity (B_max) of ⁶⁴Cu in the OE were 6.7 and 10.0 nmol Cu g^-1, respectively. As waterborne Ca²⁺ was increased from 50 to 1000 μM L^-1, the B_max of Cu decreased by ~50% while the log K _Cu-OE remained constant, indicative of noncompetitive inhibition. Using electro-olfactograms (EOG), short-term exposures to 160 and 240 nmol Cu L^-1 were found to reduce olfactory responses to 10^-5 M L-arginine by 72 and 79%, respectively. Short-term exposure to 160 nmol Cu L^-1 also caused a 15-fold reduction in behavioral responses toafood stimulus. Interestingly, increasing waterborne Ca²⁺ did not reduce the effects of Cu on EOG or behavioral responses. These results demonstrate that short-term, environmentally realistic concentrations of Cu not only bind to the OE of fathead minnows but also impair their olfactory sensitivity and behavioral responses to olfactory stimuli. Waterborne Ca²⁺ reduces Cu-OE binding but does not protect against olfactory impairment.