Until very recently, however, it was unclear whether potassium efflux directly influenced the function or activity of different effectors of apoptosis, in particular the caspase family of cystein proteases and the endonucleases that are associated with most paradigms of cell death. Using glucocorticoid-treated thymocytes, Hughes et al. have reported that inhibition of potassium efflux by disruption of the normal potassium electrochemical gradient prevents caspase-3 activation as well as endogenous nuclease activity.
Furthermore, caspase and nuclease activities were found to be restricted to those thymocytes exhibiting reduced intracellular potassium levels and cell shrinkage. This study was shortly followed by a comprehensive evaluation of potassium efflux, caspase-3 activation, nuclease activity, and cell death in S49-Neo lymphoma cells treated with a diverse spectrum of proapoptotic agents, collectively supporting the hypothesis that a net loss of potassium from the cell is in fact an early and central step in a conserved cell death program.
In the present study, we have examined the efflux of potassium during the apoptotic death of female germ cells and follicular granulosa cells and explored the consequences of preventing cytosolic potassium efflux by disrupting the potassium electrochemical gradient. Additionally, on the basis of recent studies suggesting the involvement of caspases, serine proteases, and nucleases in apoptosis in oocytes and granulosa cells, we evaluated the possibility that potassium directly modulates the activities of the enzymes required for cytoplasmic and nuclear destruction that ultimately produce the apoptotic bodies for phagocytosis. Lastly, cell-free assays were employed using purified deoxyribonuclease (DNase)-I and DNase-II, two enzymes implicated in genome fragmentation during apoptosis, as well as granulosa cell nuclear protein extracts possessing endogenous nuclease activity, to determine whether potassium affects the occurrence of DNA cleavage in ovarian cells by directly suppressing endonuclease activity.