The effects of copper on ionic regulation by the gills of the seawater-adapted flounder (Platichthys flesus L.)

Summary Potentials measured in isolated, perfused gills fromPlatichthys suggest that the electrogenic ion-pump(s) contribute significantly to the potential measured in seawater. Copper added to the perfusate causes a significant reduction in the potential measured in the isolated gill and it is suggested that this is due to a direct inhibition of the branchial ion pump(s). Vascular resistance was unaffected by the presence of copper. Ouabain-sensitive oxygen consumption was reduced in tissue exposed to copper whereas residual oxygen consumption was unaffected, which suggests that the in vitro action of copper is confined to the Na⁺, K⁺ ATPase dependent portion of branchial metabolism.In vitro application of copper to gill homogenates fromPlatichthys flesus adapted to seawater caused a marked reduction in Na⁺, K⁺ ATPase activity. In vivo a combination of ouabain binding (to determine the number of enzyme sites), together with measurements of Na⁺, K⁺ ATPase activity showed that exposure of the fish to ambient copper in seawater also inhibited enzyme activity. However this response was modulated by a reduction in the sensitivity of the enzyme to copper in copper-treated fish and also responses, possibly of an endocrine nature, modifying Na⁺, K⁺ ATPase activity and returning overall enzyme levels to values not significantly different from those in control fish.In addition, this study indicates the importance of obtaining information on both the number of enzyme sites as well as their overall activity in assessing the effects of agents modifying enzymes involved in ion transport.