The use of the mitochondrial transmembrane electric potential as an effective biosensor in ecotoxicological research

In this work, the mitochondrial transmembrane electric potential (Δ ψ) of isolated mitochondria was used to evaluate the toxicity of some chemicals (endosulfan, 3,4-dichloroaniline, parathion, tributyltin and cadmium) and wastewater. Mitochondria were isolated from rat liver, and the Δ ψʹ measured in a suitable assay medium, using a sensitive tetraphenylphosphonium (TPP+) electrode. The test substance was preincubated in a rotenone-containing medium during 3 min with l.0 mg of mitochondrial protein. Mitochondria were energised with succinate and after the establishment of a constant maximal potential ADP was added to induce the phosphorylative cycle. Chosen endpoints were the membrane potential from mitochondria oxidising succinate and the depolarisation induced by ADP. After the appropriate transformations the EC50 (effective concentration) was calculated for each toxicant. Even very low concentrations of a toxicant were able to affect the Δ ψ, thus showing its suitability as a biosensor in ecotoxicology and results were reproducible between tests. The utilisation of Δ ψ in screening tests of pure substances and wastewater seems to be very effective and can be carried out routinely.