Metal Binding Activity of the Gills of Rainbow Trout (<i>Oncorhynchus mykiss</i>)

Abstract

The objective of this study was to characterize the metal binding of the external gill surface in an attempt to interrelate metal chemistry, gill surface binding activity, and possibly metal toxicity. Individual gill arches from adult rainbow trout (Oncorhynchus mykiss) were exposed to various concentrations of either 140 La, 45 Ca, 109 Cd, or 64 Cu. The apparent dissociation constant (K D ) and capacity (B max ) of the external gill surface for the metals was calculated using Scatchard plot analysis. Half-saturation time (t 1/2 ) and binding cooperativity (H n ) were also determined. The K D for gill metal binding ranged from 0.31 ± 0.02 mM for La 3+ (high affinity) to 4.3 ± 0.04 mM for Cu 2+ (low affinity). The gill binding affinity for Ca 2+ was threefold lower than for La 3+ , but was similar to that for Cd 2+ . The gills had the lowest affinity for Cu 2+ , almost 14 times lower than that for La 3+ . B max for La 3+ was found to be significantly lower than for any other metal (0.14 ± 0.001 μmol∙g −1 ), while nearly seven times as much Cu 2+ was accumulated by the gills compared with La 3+ , The Ca 2+ and Cd 2+ B max estimates were intermediate.