Metal Binding Activity of the Gills of Rainbow Trout (Oncorhynchus mykiss)

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 ¹⁴⁰La, ⁴⁵Ca, ¹⁰⁹Cd, or ⁶⁴Cu. 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 La³⁺ (high affinity) to 4.3 ± 0.04 mM for Cu²⁺ (low affinity). The gill binding affinity for Ca²⁺ was threefold lower than for La³⁺, but was similar to that for Cd²⁺. The gills had the lowest affinity for Cu²⁺, almost 14 times lower than that for La³⁺. B_max for La³⁺ was found to be significantly lower than for any other metal (0.14 ± 0.001 μmol∙g⁻¹), while nearly seven times as much Cu²⁺ was accumulated by the gills compared with La³⁺, The Ca²⁺ and Cd²⁺B_max estimates were intermediate.