Multiple effects of DiS‐C 3 (5) on mitochondrial structure and function

3,3′‐Dipropyl‐2,2′‐thiadicarbocyanine iodide [DiS‐C 3 (5)], often used as a tracer dye to assess the mitochondrial membrane potential, was investigated in detail regarding its effects on the structure and function of isolated mitochondria. As reported previously, DiS‐C 3 (5) had an inhibitory effect on NADH‐driven mitochondrial electron transfer. On the contrary, in the presence of inorganic phosphate, DiS‐C 3 (5) showed dose‐dependent biphasic effects on mitochondria energized by succinate. At higher concentrations, such as 50 µ m , DiS‐C 3 (5) accelerated mitochondrial oxygen consumption. Measurements of the permeability of DiS‐C 3 (5)‐treated mitochondrial membranes to poly(ethylene glycol) and analysis of mitochondrial configuration by transmission electron microscopy revealed that the accelerating effect of DiS‐C 3 (5) on mitochondrial oxygen consumption reflects the induction of the mitochondrial permeability transition (PT). When the mitochondrial PT was induced by DiS‐C 3 (5), release of mitochondrial cytochrome  c was observed, as in the case of the PT induced by Ca 2+ . On the contrary, at a low concentration such as 5 µ m , DiS‐C 3 (5) showed an inhibitory effect on the latent oxygen consumption by mitochondria. This effect was shown to reflect inhibition of the PT induced by a low concentration of Ca 2+ . Furthermore, in the absence of inorganic phosphate, DiS‐C 3 (5) caused mitochondrial swelling. Under this condition, DiS‐C 3 (5) caused changes in the membrane status of the mitochondria, but did not induce a release of mitochondrial cytochrome  c .