Recent evidence, derived primarily from studies of cultured thymocytes, suggests that a major efflux of intracellular potassium occurs in the early stages of apoptosis and that this efflux is required for the activation of key components of the cell death machinery. In the present study, we undertook a series of experiments to assess potassium levels during apoptosis of ovarian germ cells and granulosa cells and the role of this ion in controlling several morphological and biochemical characteristics of cell death. Using anti-cancer drug-treated murine oocytes as a model for female germ cell apoptosis, we observed a consistent decrease in intracellular levels of potassium as the oocytes died.
As recently shown in thymocytes, placing cells in medium containing a high level of K+ prevented K+ efflux during apoptosis and blocked many features of apoptosis, such as cellular shrinkage and fragmentation. This high-K+ medium was also effective in blocking many aspects of apoptosis in oocytes and granulosa cells, suggesting similar K+-dependent apoptotic pathways in these cells. Unlike thymocytes, however, some apoptotic events in oocytes, such as DNA degradation, were not completely blocked, suggesting that both potassium-dependent and potassium-independent pathways function in germ cells to mediate different apoptotic events.