Mitochondrial membrane potential differentiates cells resistant to apoptosis in hybridoma cultures

Previous research has implicated mitochondrial physiology and, by extension, respiratory capacity in the initiation and progress of apoptosis of cells in culture and tissue environments. This hypothesis was tested by separating a hybridoma cell population into subpopulations of varying mitochondrial membrane potential (MMP) using Rhodamine 123 stain and fluorescence-activated cell sorter analysis and subjecting them to two apoptosis inducers, rotenone and staurosporin. Apoptotic death was characterized morphologically through the determination of apoptosis-related chromatin condensation and biochemically through the measurement of caspase-3 enzymatic activity. We found dramatic differences in the apoptotic death kinetics for the subpopulations, with the high MMP cells showing higher resistance to apoptotic death. After incubation with 30 microM rotenone, the low MMP cells exhibited one-third of the viability of the high MMP cells and a three-fold increase in the capsase-3 enzymatic activity. No changes were observed in the DNA content or the cell cycle distributions of the two cell subpopulations, which maintained their mean MMP difference after 20 generations. These results suggest that heterogeneity exists in mammalian cell populations with respect to mitochondrial physiology, which correlates with resistance to apoptotic death.