Effects of the mitochondrial probe rhodamine 123 and related analogs on the function and viability of pulsating myocardial cells in culture

Rhodamine 123, a cationic fluorescent dye, has previously been shown to specifically localize in or on mitochondria in living cells. Since it has also been shown to be relatively non-toxic in a variety of cell types it has been a useful tool for probing mitochondria in vitro. In this report, using cardiac cells in culture, we demonstrate that rhodamine 123 and 6G both positively charged compounds, quickly inhibit beating and kill cardiac-muscle cells while uncharged or neutral rhodamines, 116 and B, produce neither effect. We also present data which illustrate that the cationic rhodamines inhibit oxidative phosphorylation in isolated mitochondria while the neutral dyes do not. It is suggested that both phenomena may be related.