Significant correlation between refractive index and activity of mitochondria: single mitochondrion study.

Measurements of refractive indices (RIs) of intracellular components can provide useful information on the structure and function of cells. The present study reports, for the first time, determination of the RI of an isolated mitochondrion in isotonic solution using retardation-modulated differential interference contrast microscopy. The value was 1.41 ± 0.01, indicating that mitochondria are densely packed with molecules having high RIs. Further, the RIs of each mitochondrion were significantly correlated with the mitochondrial membrane potential, an index of mitochondrial activity. These results will provide useful information on the structures and functions of cells based on the intracellular distribution of RIs.