Effect of coumarins on mitochondrial function I. Uncoupling of oxidative phosphorlation.

8-Acetyl-5,7-diemthoxy-4-phenylcoumarin at concentrations 0.03 to 0.3 mM uncoupled oxidative phosphorylation, in vitro, in rat liver mitochondria. Preincubation of mitochondria with the compound enhanced this effct. Similar uncoupling was observed with 5,7-dihydroxy-4phenylcoumarin; 7-acetonyloxycoumarin; 6,7-dimethyl-4-phenylcoumarin and 4-phenyldaphentin also. All these compounds stimulated mitochondrial ATPase activity three- to eight-fold. However, coumarin, the paretn substance of all these compounds had no effect on oxidative phosphorylation in mitochondria.