The uncoupled state of traditionally isolated and tested brown adipose tissue mitochondria

The uncoupled state of traditionally isolated and tested brown adipose tissue mitochondria 

When mitochondria are isolated and tested in media which only contain osmotic support (sucrose or KCl) and a buffer (and Mg, Pj and EDTA, if necessary), they respire rapidly on substrates such as succinate or glycerol-3-phosphate (citrate, 2-oxoglutarate and malate are poor substrates in brown fat mitochondria from most species, as the substrate permeases are poorly developed [16]). This rapid respiration is seen in Fig. 10.2. This observation was initially made even before the thermogenic function of brown adipose tissue was known [17]. When R. Em. Smith had established that heat production was the function of the tissue [18], an intrinsic uncoupled state of the mitochondria [19,20] could be understood as the means of heat production, the intensity of which would be limited only by substrate supply [21]. However, Horwitz et al. [21a] found that addition of the artificial uncoupler DNP could potentiate the respiration of the tissue, and the conclusion had to be that the mitochondria — although uncoupled when isolated — were coupled in situ. 

---