Figure 5.

Comparison of mitochondrial respiratory capacity and coupling control in human sWAT, sBAT, and skeletal muscle. (a) Representative respiration experiments performed on permeabilized sWAT and sBAT from the same seven individuals and skeletal muscle from six separate individuals following the sequential titration of substrates and oligomycin as describe in Fig 1A (values are group means). (b) Comparison of respiratory states for sWAT, sBAT and skeletal muscle shown in panel a highlight similar respiratory capacity in human BAT and skeletal muscle. (c) The respiratory control ratio for ADP (RCR_ADP) calculated by dividing state 3_I by state 2. A RCR_ADP < 1 indicates that mitochondria are not coupled in human sBAT. (d) The coupling control ratio for oligomycin (CCR_OM) calculated by dividing state 4_O by state 3_I+II. A CCR_OM of = 1 indicates that mitochondria are insensitive to oligomycin and thus are uncoupled. A lower CCR_OM suggest better coupled mitochondria in sWAT and skeletal muscle. (e) Representative respiration experiments performed on permeabilized sWAT, sBAT and skeletal muscle from the same individuals in panel a following the sequential titration of substrates (1.5 mM octanoyl-l-carnitine, 5 mM pyruvate, 2 mM malate, and 10 mM glutamate), ADP (5 mM), succinate (10 mM), cytochrome C (10 μM) and the ionophore CCCP (5 μM) (values are group means). (f) Comparison of respiratory states for sWAT, sBAT and skeletal muscle shown in panel e again showing that sBAT has a respiratory capacity more akin to that of muscle than sWAT in humans. (g) The leak control ratio (LCR), calculated by dividing state 3_I+II by state 3_U, shows the absence of leak control in human sBAT. The lux control ratio (FCR), an index of the efficiency of the oxidative phosphorylation system, was calculated by dividing state 2 by state 3_U. A lower FCR in BAT demonstrates poor mitochondrial coupling control. Note that while the addition of ADP to sBAT reduces leak respiration there is also likely a stimulation of coupled respiration (ATP production). However, this is minimal given the blunted response to the ATP synthase inhibitor oligomycin observed in coupled sBAT mitochondria. Note that leak respiration prior to titration of substrates is supported by endogenous substrates, likely FFAs. Values are presented as means ± SE unless otherwise stated. *P<0.05 vs. sWAT; **P<0.01 vs. sWAT; ***P<0.001 vs. sWAT; ^†P<0.05 vs. sBAT; ^††P<0.01 vs. sBAT; ^†††P<0.001 vs. sBAT.