Figure 6. 3OHB augments respiratory efficiency in isolated heart mitochondria.
Freshly isolated mitochondria from heart ventricles of C57BL/6N mice were utilized to assess the impact of 3-hydroxybutyrate (3OHB) on the relationship between (A) oxygen consumption rate (JO2) (B) mitochondrial membrane potential (ΔΨ) in millivolts (mV), and (C) NAD(P)H/NAD(P)+ redox state versus the estimated Gibbs energy of ATP hydrolysis (ΔGATP). Mitochondria were fueled with pyruvate + malate (P/M, 110 μM each) and increasing concentrations of L-octanoylcarnitine (OC; 10, 50, or 100 μM) in the absence (purple) or presence (red) of 2 mM 3OHB. (D) Mitochondrial respiratory efficiency was evaluated by plotting JO2 against ΔΨ in the presence of P/M + 10–100 μM OC ± 3OHB. Dotted lines separate the submaximal and maximal portions of JO2 vs. ΔGATP. Triangle denotes the changing concentrations of ATP relative to ADP (ATP/ADP), resulting in a reciprocal change in energy demand. Data are mean ± SEM (n = 5). Measurements made at submaximal JO2 (A–C) were analyzed by 2-way ANOVA (†main effect of ketone; ‡ketone, ΔGATP interaction; P < 0.05), whereas those representing maximal JO2 (ΔGATP = –12.95) were analyzed via t test (*P < 0.05).