Copper uptake across rainbow trout gills

Abstract

SUMMARY: Several components of branchial copper uptake were identified in juvenile freshwater rainbow trout (Oncorhynchus mykiss) using 64Cu. On the basis of competitive interactions between sodium and copper uptake,inhibition of copper uptake by a proton pump inhibitor (bafilomycin A1, 2μmol l-1) and a Na+ channel blocker (phenamil, 100μmol l-1), it appears that a proportion of the branchial copper uptake occurs via an apical Na+ channel. This sodium-sensitive copper uptake demonstrates saturation kinetics, with a Km of 7.1 nmol l-1 and a Jmax of 21.2 pmol g-1 h-1, and is characterized by an IC50 of 104 μmol l-1 sodium. On the basis of residual copper uptake in the presence of high sodium concentrations (20 mmol l-1) and differential inhibition of sodium and copper uptake by phenamil (100 μmol l-1), a sodium-insensitive component of copper uptake is also present in trout gills. It demonstrates saturation kinetics with a comparably low Km (9.6 nmol l-1) but a lower maximum transport capacity (Jmax=3.5 pmol g-1 h-1)than the sodium-insensitive system. Sodium uptake exhibits saturation kinetics with a Km of 69 μmol l-1. Copper reduced branchial sodium transport affinity but increased the maximal sodium transport capacity.