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 i ndirect actions of the metal mediated via the stress hormone cortisol, a 24 h in vitro gill filament culture was used to investigate the eff ects of this heavy metal and hormone, singly and in combination, on ap optosis and necrosis of chloride cells in the cichlid fish, tilapia (O reochromis, mossambicus). Cell death was identified after fluorescent double-labelling using a confocal laser scanning microscope. Incubatio n 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 c ompared 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 CuSO 4 reduced necrosis by about 75%. The apparent protection provided by c ortisol against copper toxicity could be blocked by the glucocorticoid receptor blocker RU 486. Incubation with 0.83 mu M cortisol induced a poptosis to the same extent as that of camptothecin, a topoisomerase I inhibitor. We conclude that Cu directly causes necrosis of chloride c ells, whilst cortisol protects against copper toxicity at lower concen trations, and induces apoptosis at higher concentrations, typical for severely stressed fish. (C) 1998 Elsevier Science B.V.