Rhodamine 123: is it an appropriate dye to study P-glycoprotein activity in adriamycin-resistant K562 cells?

The ability of the P-glycoprotein to efflux rhodamine 123 and adriamycin was evaluated using adriamycin-sensitive and -resistant human leukemia K562 cells. We observed that low temperature or verapamil (a P-glycoprotein blocker) inhibited adriamycin efflux in multidrug resistant cells. In the same conditions, resistant K562 cells did not significantly retain rhodamine 123. This dye was located in the cytoplasm of resistant cells and did not display spectral properties characteristic of stacked rhodamine 123 molecules in mitochondria of sensitive K562 cells. Thus, in adriamycin-resistant K562 cells, the rhodamine efflux may be due to P-glycoprotein activity and also to a nonspecific targeting of dye in resistant K562 cells.