Inhibition of Na<sup>+</sup>/K<sup>+</sup>-ATPase may be one mechanism contributing to potassium efflux and cell shrinkage in CD95-induced apoptosis
Nobel CSI., Aronson JK., Van Den Dobbelsteen DJ., Slater AFG.
To investigate the involvement of K + efflux in apoptotic cell shrinkage, we monitored efflux of the K + congener, 86 Rb + , and cell volume during CD95-mediated apoptosis in Jurkat cells. An anti-CD95 antibody caused apoptosis associated with intracellular GSH depletion, a significant increase in 86 Rb + efflux, and a decrease in cell volume compared with control cells. Preincubating Jurkat cells with Val-Ala-Asp-chloromethylketone (VAD- cmk), an inhibitor of caspase proteases, prevented the observed 86 Rb + efflux and cell shrinkage induced by the anti- CD95 antibody. A wide range of inhibitors against most types of K + channels could not inhibit CD95-mediated efflux of 86 Rb + , however, the uptake of 86 Rb + by Jurkat cells was severely compromised when treated with anti-CD95 antibody. Uptake of 86 Rb + in Jurkat cells was sensitive to ouabain (a specific Na + /K + -ATPase inhibitor), demonstrating Na + /K + -ATPase dependent K + uptake. Ouabain induced significant 86 Rb + efflux in untreated cells, as well as it seemed to compete with 86 Rb + efflux induced by the anti-CD95 antibody, supporting a role for Na + /K + -ATPase in the CD95-mediated 86 Rb + efflux. Ouabain treatment of Jurkat cells did not cause a reduction in cell volume, although together with the anti-CD95 antibody, ouabain potentiated CD95-mediated cell shrinkage. This suggests that the observed inhibition of Na + /K + -ATPase during apoptosis may also facilitate apoptotic cell shrinkage.