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

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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 (KD) and capacity (Bmax) of the external gill surface for the metals was calculated using Scatchard plot analysis. Half-saturation time (t1/2) and binding cooperativity (Hn) were also determined. The KD 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+. Bmax 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+Bmax estimates were intermediate.

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