Pump and channel K+ (Rb+) fluxes in apoptosis of human lymphoid cell line U937

Ouabain-sensitive (OS) and -resistant (OR) Rb+ influx was examined in three sublines of U937 cells to compare alterations of K+ channel permeability and the Na+, K+-ATPase pump leading to the shift in ion and water balance during apoptosis induced by 0.2 and 1 mu M staurosporine (STS) for 4-5 h. Cell K+, Rb+, Na+ and Cl- content was determined by flame photometry and Cl-36 distribution. Changes in cell water content were monitored by measurement of buoyant cell density and distribution of [H-3]-glycerol or 3-O-methyl-D-[H-3] glucose. Apoptosis was detected by DNA flow cytometry and light microscopy of the native cells stained with acridine orange. Treatment with 0.2 mu M STS for 5 hours led to mild apoptosis with 10-13 % cell dehydration and either moderate increase of channel mediated Rb+ influx without significant changes in the pump activity or moderate decrease of pump Rb+ influx without significant change of channel influx, depending on the cell line used. Treatment with 1 mu M STS was followed by 18-23 % cell dehydration, a decrease of the pump activity and a small or insignificant increase in the OR Rb+ influx in all studied sublines. It is concluded that moderate apoptotic cell shrinkage may be associated with both an increase in K+ channel permeability and inhibition of the pump whereas more remarkable shrinkage occurs presumably due to inhibition of the pump. Copyright (C) 2008 S. Karger AG, Basel.