We present here a confocal fluorescence microscopy study of mitochondria in sensitive and resistant
carcinoma cells by using two potentiometric probes of mitochondria,
rhodamine 123 (R123) and dimethylaminostyryl-methylpyridiniumiodine. We have found that active mitochondria in sensitive MCF-7 and multidrug resistant MCF-7/DX
carcinoma cells are very different in localization and morphology. In sensitive cells active mitochondria are found in the perinuclear region, whereas in the multidrug resistance (MDR) subline they are confined to the cell periphery. Interestingly, the MDR revertant
verapamil has been found to restore in MCF-7/DX cells the same pattern of active mitochondria seen in sensitive cells. We have also studied R123 in human lung
carcinoma A549 cells, which display a low responsivity to
doxorubicin, and overexpress the lung resistance-related
protein. In addition to perinuclear mitochondria, peripheral mitochondria with weaker fluorescence can be seen in this cell line. Interestingly, in the two examined
carcinoma lines we have been able to recognize by image analysis a common new star-lobed morphology. Our results indicate that in resistant
carcinoma cells two populations of mitochondria coexist with different localization, morphology, and activity.