Uncoupling of oxidative phosphorylation in rat liver mitochondria by chloroethanols

Chloroethanols are toxic chemicals used in industry and also formed as a result of the metabolism of several widely used halogenated hydrocarbons. The effect of 2-chloroethanol (CE), 2,2-dichloroethanol (DCE) and 2,2,2-trichloroethanol (TCE) on rat liver mitochondrial respiration was studied. Rat liver mitochondria were isolated in a medium consisting of 250 mM sucrose, 10mM Tris-HCl and 1 mM EDTA (pH 7.4). Mitochondrial respiration was determined with an oxygen electrode at 30 degrees C and the polarographic buffer consisted of 250 mM mannitol, 10 mM KCl, 10 mM K2HPO4, 5 mM MgCl2, 0.2 mM EDTA and 10 mM Tris-HCl (pH 7.4). With succinate as the respiratory substrate and using chloroethanols (150 mM), CE stimulated respiration by 28.2 +/- 6.5% and DCE by 202.7 +/- 8.2% while TCE inhibited mitochondrial respiration (greater than 95%). The effect of change in the concentration of chloroethanols on mitochondrial respiration was also studied. CE showed maximum stimulation at 600 mM (97.6%), DCE at 150 mM (202.6%) and TCE at 30 mM (313.6%). Respiratory stimulation was independent of mitochondrial protein concentration. Chloroethanols (optimal concentrations for respiratory stimulation with succinate) inhibited mitochondrial respiration when glutamate-malate was used as the respiratory substrate. Estimation of adenosine triphosphate (ATP) showed that chloroethanols inhibited the synthesis of ATP. These results indicate that chloroethanols stimulate mitochondrial respiration by uncoupling oxidative phosphorylation and that the uncoupling potency is proportional to the extent of chlorination at the beta-position of haloethanol.