Differentiation of promyelocytic (HL-60) cells into mature granulocytes: mitochondrial-specific rhodamine 123 fluorescence.

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Abstract
Rhodamine 123, a fluorescent dye which binds as a result of the transmembrane potential, was used to stain the mitochondria of HL-60 cells, a cell line established from human promelocytic leukemia cells. The DMSO[dimethylsulfoxide]-induced differentiation of promyelocytic cells into mature granulocytes caused a 4-fold decrease in fluorescence intensity that paralleled the disappearance of S-phase and G2M cells. Upon myeloid differentiation whereby the cells enter an irreversible quiescent state, the mitochondrial mass of the cells apparently has decreased. This suggestion is corroborated by EM, which shows a decrease in the number of mitochondria, and by decreases in total mitochondrial protein and cytochrome oxidase activity. The respiratory rate of isolated mitochondria did not change, suggesting that the transmembrane potential remained the same. Undifferentiated cells in exponential phase of growth exhibit an intracellular heterogeneity of fluorescence intensity. This heterogeneity appears to have a cell age basis, as late S/G2M cells, obtained by centrifugal elutriation, yielded twice the fluorescence intensity of early G1 cells.