Cell-membrane integrity of chinese hamster ovary cells on exposure to saponin. Immobilized cells were exposed for 30 s to saponin guided hydrodynamically into 200-μm-wide lanes (arrow indicate the direction of flow). Calcein AM and ethidium homodimer-1 were then applied in the same positions of the flow chamber. Calcein AM enters all cells, and is enzymatically converted to green-fluorescent calcein in the cytoplasm. Cells with an intact plasma membrane (viable cells) retain calcein, and thus fluoresce green. Only cells with a compromised plasma membrane (dead cells) take up ethidium homodimer-1. The red fluorescence of ethidium homodimer-1 is strongly enhanced once it interacts with the nucleic acids of the cell. The ratio of dead (red) to viable (green) CHO cells increased with increasing concentration of saponin. Scale bar, 100 μm.