The analysis of drug action on mitochondrial oxidative phosphorylation. The choice of organic solvent for water-insoluble drugs.

Four organic solvents were tested for their ability to interfere with ADP- and 2,4-dinitrophenol-stimulated respiration in tightly-coupled guinea-pig liver mitochondria. All four compounds inhibited mitochondrial respiration, but dimethylformamide and ethanol were more potent than dimethylsulphoxide and propyleneglycol. The latter compound was the only one that failed to produce a significant inhibition of the reactions. Using dimethylformamide, it was shown that inhibition of the reactions was independent of the substrates employed. A detailed analysis was made of the effect of a range of concentrations of dimethylformamide on the uncoupling activity of a range of concentrations of 2,4-dinitrophenol. It was clearly demonstrated that the inclusion of dimethylformamide in the reaction medium would result in an underestimate of the activity of dinitrophenol. Recommendations are made concerning the precautions that should be taken when analysing the effects of water-insoluble drugs on oxidative phosphorylation.