CoQ is deficient in cardiac mitochondria of apoA1 null mice and is normalized by supplementation (A). Mitochondria were isolated by differential centrifugation from the hearts of WT or apoA1 null mice supplemented with CoQ10 or not by i.p. injection daily for 3 d before harvest (mean ± SD; n = 3 per group; *P < 0.05 vs. other groups). CoQ10 concentrations were quantitated after extraction by HPLC and UV absorption in relation to a CoQ9 internal standard. Representative Western blot (performed 3 times) for cytochrome oxidase in different groups shows that mitochondrial mass is not altered among groups or by CoQ10 supplementation (B). APOA-I KO, apoA1 null mice; CoQ, coenzyme Q; CoQ10, coenzyme Q10; COX IV, cytochrome c oxidase subunit IV; WT, wild-type mice.