Cortisol protects against copper induced necrosis and promotes apoptosis in fish gill chloride cells in vitro

In order to distinguish between toxic actions of copper (Cu) and the indirect actions of the metal mediated via the stress hormone cortisol, a 24 h in vitro gill filament culture was used to investigate the effects of this heavy metal and hormone, singly and in combination, on apoptosis and necrosis of chloride cells in the cichlid fish, tilapia (Oreochromis, mossambicus). Cell death was identified after fluorescent double-labelling using a confocal laser scanning microscope. Incubation of filaments with 50 mu M and 100 mu M CuSO4 caused an approximate 5- and 16-fold increase, respectively, in chloride cell necrosis when compared to control, but had no significant effect on apoptosis. A 12 h incubation with 0.28 mu M cortisol prior to exposure to 100 mu M CuSO4 reduced necrosis by about 75%. The apparent protection provided by cortisol against copper toxicity could be blocked by the glucocorticoid receptor blocker RU 486. Incubation with 0.83 mu M cortisol induced apoptosis to the same extent as that of camptothecin, a topoisomerase I inhibitor. We conclude that Cu directly causes necrosis of chloride cells, whilst cortisol protects against copper toxicity at lower concentrations, and induces apoptosis at higher concentrations, typical for severely stressed fish. (C) 1998 Elsevier Science B.V.