Nile red labeling of single living cells for contour delineation to quantify and evaluate the distribution of rhodamine 123 with fluorescence image cytometry.

Simultaneous study of intracellular quantification and distribution of fluorescent probes is difficult when cell staining is not homogeneous. This occurs after mitochondrial staining with rhodamine 123 (R123). Classical techniques for evaluation of intracellular R123 fluorescence, such as flow cytometry, are based on measurement of the global fluorescence intensity but do not take into account parameters that reflecting cellular distribution of the probe. For simultaneously studying intracellular quantification and distribution of R123 with fluorescence image analysis, we delineated a mask of the cell, generated from a fluorescent image of the plasma membrane stained by nile red (NR). After a preliminary study of the fluorescence characteristics of R123 and NR to avoid artifacts and optimize conditions of staining, quantification and distribution of intracellular R123 studies were performed by superimposition of the mask on the R123 fluorescence image. This protocol was applied to leukemic cells and allowed estimation of individual cell parameters such as mean fluorescence intensity and standard deviation, the latter providing information of the cellular distribution of R123. Moreover, it permitted demonstration of the redistribution of R123 in the whole cell when coincubated in the presence of nigericin.