Rhodamine 123 as a probe of in vitro toxicity in MDCK cells.

The effect of mercuric chloride on Madin-Darby Canine Kidney (MDCK) cells grown in culture was assayed by the mitochondrial-specific fluorescent probe, rhodamine 123. Treatment of cells with mercuric chloride resulted in a dissipation of rhodamine fluorescence from the mitochondria into the cytoplasm, followed by a release into the medium bathing the cells. Toxicity was assayed either by determining the proportion of cells with delocalized rhodamine fluorescence, or by measuring the rhodamine released from or retained in the cells. Quantifying the release or retention of rhodamine 123 is semi-automated and represents a highly sensitive method of using a vital fluorescent dye for in vitro toxicity analysis.