Plasma membrane depolarization without repolarization is an early molecular event in anti-Fas-induced apoptosis

The movement of intracellular monovalent cations has previously been shown to play a critical role in events leading to the characteristics associated with apoptosis. A loss of intracellular potassium and sodium occurs during apoptotic cell shrinkage establishing an intracellular environment favorab le for nuclease activity and caspase activation. We have now investigated t he potential movement of monovalent ions in Jurkat cells that occur prior t o cell shrinkage following the induction of apoptosis. A rapid increase in intracellular sodium occurs early after apoptotic stimuli suggesting that t he normal negative plasma membrane potential may change during cell death, We report here that diverse apoptotic stimuli caused a rapid cellular depol arization of Jurkat T-cells that occurs prior to and after cell shrinkage. In addition to the early increase in intracellular Na+, Rb-86(+) studies re veal a rapid inhibition of K+ uptake in response to anti-Fas. These effects on Na+ and K+ ions were accounted far by the inactivation of the Na+/K+-AT Pase protein and its activity. Furthermore, ouabain, a cardiac glycoside in hibitor of the Na+/K+-ATPase, potentiated anti-Fas-induced apoptosis. Final ly, activation of an anti-apoptotic signal, i.e. protein kinase C, prevente d both cellular depolarization in response to anti-Pas and all downstream c haracteristics associated with apoptosis. Thus cellular depolarization is a n important early event in anti-Pas-induced apoptosis, and the inability of cells to repolarize via inhibition of the Na+/K+-ATPase is a likely regula tory component of the death process.