Effect of nitric oxide (NO) donors on mitochondrial membrane potential. (A) Fluorescence-activated cell sorter analysis of mitochondrial membrane potential in human chondrocytes. Untreated and treated normal chondrocytes with NO donors were stained with 5,5',6,6'- tetrachloro-1,1',3,3'-tetraethylbenzimidazole carbocyanide iodide (JC-1) and analysed by flow cytometry. Photomultiplier settings were adjusted to detect JC-1 monomer fluorescence signals on the filter 1 (FL1) detector (green fluorescence) and JC-1 aggregate fluorescence signals on the FL2 detector (red fluorescence). Shown is an example of chondrocytes treated with 1 mM SNP and 2 mM N-ethyl-2(1-ethyl-2 hydroxy-2-nitrosohydrazine (NOC-12) for 24 hours. (B) Quantification of red and green fluorescence. Histograms represent the JC-1 fluorescence of normal cells and those treated with NO donors. Green fluorescence (open graph) increases, whereas red fluorescence (solid graph) decreases in the NOC-12 and sodium nitroprusside (SNP)-treated chondrocytes, suggesting a reduction of the mitochondrial membrane potential, and therefore, a decrease in the red/green ratio. Shown is an example at 24 hours. Results are the mean ± SD; n = 5. *P ≤ 0.05 versus untreated chondrocytes (control).