Inhibition of mitochondrial oxidative metabolism by SKF-525a in intact cells and isolated mitochondria

We have examined the effects of various concentrations of SKF-525A (β-diethylamino-ethyldiphenylpropyl acetate · HCl) on the energy metabolism of l and two types of ascites tumor cells, as well as on ion transport in liver slices. In liver slices, 0.2 to 1.0 mM SKF-525A caused an initial stimulation of O₂ uptake which was followed, at 0.5 to 1.0 mM, by a progressive inhibition of O₂ consumption, a fall of slice ATP content, and a reduced transport of K⁺, Na⁺ and Ca²⁺. In isolated mitochondria, we studied the effects of SKF525A on the rate of respiration and on the oxidation-reduction responses of NAD(P)⁺ and cytochrome b in the presence of various substrates. The results suggest that SKF-525A had three distinct actions on liver mitochondria, viz. an uncoupling action at low concentrations (0.02 to 0.17 mM); at higher concentrations (0.2 to 0.5 mM) an inhibition of the oxidation of NAD(P)⁺-linked substrates, exerted close to the substrate level; also at 0.2 to 0.5 mM, a less effective inhibition of electron transfer at a point between cytochrome b and O₂ in the electron-transfer chain. Experiments on O₂ consumption and cytochrome b oxidation-reduction changes in ascites cells showed only the first two of these effects in the intact tumor cells. We conclude that inhibition of mitochondrial energy-conserving reactions by SKF-525A can have a marked influence on energy-requiring aspects of liver-cell metabolism, one example of which is inhibition of cation active transport.