Interaction of rhodamine 123 with mitochondria isolated from drug-sensitive and -resistant Friend leukemia cells.

Mitochondria isolated from Friend leukemia cell lines sensitive (FS) and resistant (FR) to rhodamine 123 (Rho123), showed respiratory control and ADP/O ratios indicative of well-coupled oxidative phosphorylation activity. When Rho123 was added to mitochondria from both cell lines, respiratory State 4 increased. The increase was higher in mitochondria isolated from resistant than from sensitive cells. Respiratory State 3 was slightly more inhibited by Rho123 in resistant than in sensitive cell mitochondria (98 and 82% inhibition, respectively). While it is not clear how the uncoupling-like effects of Rho123 on State 4 contribute to cellular toxicity, our results indicate that differential cellular sensitivity to the drug does not correlate with inhibition of oxidative phosphorylation in mitochondria isolated from drug-sensitive and -resistant cells.