Fig. 9. Relative reduction in (A) cell Na⁺ and (B) cell K⁺ content in 800 µmol l^–1 Cu_o, normalised, against the Na⁺ content of cells treated with the appropriate drug with no added Cu. 100 µmol l^–1 phenamil (black bars), 2 mmol l^–1 amiloride (grey bars), or 10 µmol l^–1 CDPC (hatched bars), compared to drug containing controls without Cu (white bars, normalised to 100%). Values are means ± S.E.M. of N=5–6 separate experiments using fresh cells from different individual fish. Significant modulatory effect of Cu_o on the ability of the drug to reduce cell electrolyte content (Kruskal–Wallis test, P=<0.05). Amiloride is relatively more effective than other ENaC inhibitors at reducing cell Na⁺ content in the presence of Cu_o. No Cu_o-dependent modulation of drug effects on cell K⁺ occurred.