2-(Dimethylaminostyryl)-1-ethylpyridinium iodide: a fluorescent probe of energetic conditions in brown-adipose-tissue mitochondria.

2-(Dimethylaminostyryl)-1-ethylpyridinium iodide is shown to be a fluorescent monitor for the energetic state of isolated brown-adipose-tissue mitochondria. A reproducible fluorescence parameter of mitochondrial coupling conditions is established by relating the fluorescence intensity as measured under specific experimental conditions to the maximum fluorescence response displayed by the mitochondria under state 4-conditions in the presence of albumin and GDP. Relative fluorescence intensity is a sensitive support for studies of factors regulating energetic conditions of brown-adipose-tissue mitochondria, such as albumin, nucleotides and the medium pH. Relative fluorescence intensity reflects the thermogenic state of the mitochondria and is thus characteristic for adaptive and developmental alterations of the non-shivering thermogenic activity of animals from which brown adipose tissue is taken. A possible interpretation of the observed fluorescence changes is discussed.