HG(II)-INDUCED RENAL CYTOTOXICITY - IN-VITRO AND IN-VIVO IMPLICATIONSFOR THE BIOENERGETIC AND OXIDATIVE STATUS OF MITOCHONDRIA

The effects of Hg(II) on bioenergetic and oxidative status of rat rena l cortex mitochondria were evaluated both in vitro, and in vivo 1 and 24 h after treatment of animals with 5 mg HgCl2/kg ip. The parameters assessed were mitochondrial respiration, ATP synthesis and hydrolysis, glutathione content, lipid peroxidation, protein oxidation, and activ ity of antioxidant enzymes. At low concentration (5 mu M) and during a short incubation time, Hg(II) uncoupled oxidative phosphorylation whi le at slightly higher concentration or longer incubation time the ion impaired the respiratory chain. The rate of ATP synthesis and the phos phorylation potential of mitochondria were depressed, although inhibit ion of ATP synthesis did not exceed 50%. In vivo, respiration and ATP synthesis were not affected 1 h post-treatment, but were markedly depr essed 24 h later. ATP hydrolysis by submitochondrial particle FoF1-ATP ase was inhibited (also by no more than 50%) both in vitro, and in viv o 1 and 24 h post-treatment. Hg(II) induced maximum ATPase inhibition at about 1 uM concentration but did not have a strong inhibitory effec t in the presence of Triton X-100. Oxidative stress was not observed i n mitochondria 1 h post-treatment. However, 24 h later Hg(II) reduced the GSH/GSSG ratio and increased mitochondrial lipid peroxidation and protein oxidation, as well as inhibited GSH-peroxidase and GSSG-reduct ase activities. These results suggest that the following sequence of e vents may be involved in Hg(II) toxicity in the kidney: (1) inhibition of FoF1-ATPase, (2) uncoupling of oxidative phosphorylation, (3) oxid ative stress-associated impairment of the respiratory chain, and (4) i nhibition of ATP synthesis.