EFFECTS OF COPPER ON GILL STRUCTURE AND TRANSPORT FUNCTION IN THE RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

Effects of copper were studied in freshwater adapted rainbow trout usi ng the perfused head preparation. In its monovalent chemical form, cop per at millimolar concentrations had no significant effects on Na+ and water transport. By contrast, the divalent form produced an increase in gill perfusion pressure, a significant reduction in Na+ influx and water fluxes and reversed Na+ net flux. Observations by light microsco py showed important cell damage (oedema, mucus production, cellular de squamation). By electron microscopy there was smoothing of apical memb ranes, swelling of the tubular system and destruction of mitochondria. The Na, K-ATPase activity was totally suppressed and residual ATPase activity largely inhibited by 1 mM Cu2+. There was inhibition of the N a,K-ATPase activity with an IC50 Of similar to 10 mu M of total copper (free and bound cupric fractions). As active sodium transport is loca ted on the secondary lamellae, our results show that its entry mechani sm is inhibited at that level by cupric ions only. Results are discuss ed in relation to hydromineral balance of the trout.