Production of superoxides and nitric oxide generation in haemocytes of mussel Mytilus galloprovincialis (Lmk.) after exposure to cadmium: A possible involvement of Na super(+)/H super(+) exchanger in the induction of cadmium toxic effects

摘要

The present study investigates cadmium (Cd) ability to enhance superoxides (?O sub(2) super(-)) and nitric oxide (NO) production (as nitrites) in haemocytes of mussel Mytilus galloprovincialis as well as the possible involvement of Na super(+)/H super(+) exchanger (NHE) in the induction of NADPH oxidase and NO synthase activity. PMA, a well-known PKC-mediated NADPH oxidase as well as NO synthase stimulator was also used, in order to verify Cd effects on both ?O sub(2) super(-) and NO generation. According to the results of the present study, micromolar concentrations of Cd (0.05, 5, 10 and 50 mu M) seemed to enhance ?O sub(2) super(-) and NO generation in haemocytes of mussels. Moreover, ?O sub(2) super(-) and NO generation in haemocytes exposed to Cd could be enhanced by its ability to induce reactive oxygen species (ROS) but respiratory burst activation as well. Inhibition of NO synthase with 10 mu M l-NAME, significantly attenuated Cd ability to enhance ?O sub(2) super(-) production and diminished NO generation, thus leading to the suggestion that Cd toxic effects, started at concentration of 50 mu M, could enhance NADPH oxidase and NO synthase stimulation in haemocytes of mussels. NHE seems to play a regulatory role in the induction of either ?O sub(2) super(-) or NO generation in haemocytes exposed to the metal, since its inhibition with the use of 10 mu M EIPA significantly decrease both ?O sub(2) super(-) and NO production. The involvement of NHE in the induction of ?O sub(2) super(-) and NO generation, probably via PKC-mediated NADPH oxidase and NO synthase activation, is likely to be crucial to haemocytes exposed to heavy metals, such as Cd.