Mito-pH2 fluorescent images from confocal imaging reveal heterogeneity in mitochondrial pH, even in unstimulated cells (Figure A, D for representative images). Non-uniform Mito-ph2 fluorescence was observed when comparing one cell to another, suggesting intercellular heterogeneity in pH levels. Variations are also seen within single cells, where individual mitochondria appear to differ in terms of pH levels. Heterogeneity was observed even after extracellular treatment with Ammonium Chloride (Figure ) or Sodium acetate (Figure ). This heterogeneity can also easily be seen in the distribution of Mito-pH2 fluorescence intensities as seen in confocal micrographs (Figure C,F). The variability in pH implies a diverse local micro-environment within mitochondria, possibly playing a role in regulating mitochondrial function.