Kinetic analyses of waterborne Ca and Cd transport and their interactions in the gills of rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens), two species differing greatly in acute waterborne Cd sensitivity.

Abstract

We evaluated the differential nature of interactions between waterborne Ca and Cd transport in the gills of yellow perch (Perca flavescens) and rainbow trout (Oncorhynchus mykiss), two species with a more than 400-fold difference in acute waterborne Cd tolerance. The Jmax (maximum rate of uptake) and K(m) (inverse of affinity) for Ca uptake, in the absence of Cd, were significantly lower in yellow perch (120.48 nM g(-1) wet wt h(-1) and 92.17 microM, respectively) relative to rainbow trout (188.68 nM g(-1) wet wt h(-1) and 243.90 microM, respectively). Similarly, the Jmax for Cd uptake, at the lowest waterborne Ca level (100 microM) tested, was significantly lower in yellow perch (0.27 nM g(-1) wet wt h(-1)) relative to rainbow trout (0.40 nM g(-1) wet wt h(-1), but no significant difference was observed in the K(m) values between the two species (yellow perch: 32.47 nM; rainbow trout: 31.27 nM). Waterborne Cd (0-890 nM) as well as waterborne Ca (100-1,000 microM) competitively inhibited branchial uptake of each other in both species. However, analyses of inhibitor constants for branchial Ca uptake by waterborne Cd (Ki[Cd2+]) revealed that the inhibition was about 1.8 times more potent in rainbow trout compared to yellow perch. In contrast, analyses of inhibitor constants for branchial Cd uptake by waterborne Ca (Ki[Cd2+]) indicated that the inhibition was more than three fold more potent in yellow perch than in rainbow trout. Higher branchial Ca uptake and more potent inhibition by Cd as well as higher branchial Cd uptake and less potent inhibition by Ca were also reflected in whole-body measurements of Ca and Cd influx in trout relative to perch. Overall, whole-body effects were in accord with the branchial kinetic analyses. These results further strengthen the conclusion that branchial influxes of Ca and Cd occur through common pathways. Moreover, interspecific differences in acute waterborne Cd sensitivity can be explained, at least in part, by the differential nature of interactions between waterborne Ca and Cd transport in fish gills.