Fig. 1. Simultaneous imaging (co-localization) of mitochondrial flavoproteins (A) and calcium (B) in permeabilized cardiomyocytes loaded with Rhod-2. (A) Autofluorescence of mitochondrial flavoproteins in a fully oxidized state in the absence of mitochondrial substrates shows a regular arrangement of mitochondria in saponin-permeabilized cells. (B) Fluorescence of Rhod-2 trapped in mitochondria allows the localization and quantification of mitochondrial free calcium. Clear co-localization of flavoproteins (green fluorescence) and mitochondrial calcium (red fluorescence) can be seen.