In yeast the use of rhodamine 123 (Rh123) has been restricted to the
evaluation of mitochondrial respiratory function including the discrimination
between respiratory-competent and -deficient cells. This study describes the
optimization and validation of a low-concentration Rh123 staining protocol for
the flow-cytometric assessment of mitochondrial membrane potential (∆Ψm)
changes in whole yeast cells. The optimized protocol was validated by the use
of compounds that specifically affect mitochondrial energetics.
Epifluorescence microscopy was used to monitor Rh123 distribution within the
cell. Incubation of yeast cell suspensions with Rh123 (50 nM, 10 min) gave
minimal non-specific binding and cytotoxicity of the dye. The ratio (R) between
the green fluorescence and forward scatter (both measured as log values) was
used to measure ∆Ψm with only little dependence on cell ‘volume ’ and
mitochondrial concentration. Cells treated with mitochondrial membrane deor
hyper-polarizing agents displayed a decrease and an increase of R values
respectively, indicating that changes of the Rh123 distribution in cells indicate
variations in the ∆Ψm. Live and dead cells also displayed significantly different
R values. The method described here allows assessment of ∆Ψm changes in
whole yeast cells in response to a given drug. Moreover, the relationship
between drug effects and disorders of mitochondrial energetics might be
addressed.