Suicidal Erythrocyte Death Following Cellular K⁺ Loss

Abstract

Hallmarks of apoptosis include cell shrinkage, which is at least partially due to cellular K⁺ loss. The decline of cellular K⁺ concentration has been suggested to participate in the triggering of apoptosis. Suicidal erythrocyte death or eryptosis is triggered by increased cytosolic Ca²⁺ activity leading to activation of Ca²⁺-sensitive K⁺ channels with subsequent cellular K⁺ loss and cell shrinkage, and to Ca²⁺-sensitive scambling of the cell membrane with subsequent phosphatidylserine (PS) exposure at the cell surface. Phosphatidylserine exposing erythrocytes are recognized by macrophages, engulfed, degraded and thus cleared from circulating blood. The present study explored whether cellular loss of K⁺ and/or cell shrinkage actively participate in the triggering of cell membrane phospholipid scrambling. Cellular K⁺ loss was achieved by treatment of human erythrocytes with the K⁺ ionophore valinomycin (1 nM) at different extracellular K⁺ concentrations (5-125 mM) and osmolarities (300-550m Osm). Cell volume was estimated from forward scatter and PS exposure from annexin V binding in FACS analysis. Treatment with 1 nM valinomycin indeed decreased forward scatter and increased annexin V binding. The effect was significantly blunted in the presence of staurosporine (1 µM). Increase of extracellular K⁺ concentration gradually blunted the decrease of forward scatter but inhibited annexin V binding only at extracellular K⁺ concentrations ??75 mM. An increase of extracellular osmolarity (+150 mM or 250 mM sucrose) reversed the protective effect of 75 mM KCl during valinomycin treatment. A correlation between forward scatter and annexin binding at different osmolarities and K⁺ concentrations suggests that the cellular K⁺ content determines the rate of suicidal erythrocyte death primarily through its influence on cell volume.

Lipopeptides in the Triggering of Erythrocyte Cell Membrane Scrambling

“…The cell shrinkage then contributes to the triggering of cell membrane scrambling [42]. However, surprisingly, Pam3CSK4 had no significant effect on the forward scatter.…”

Enhanced insulin sensitivity of gene-targeted mice lacking functional KCNQ1

“…The stimulation of cellular K ϩ uptake was shown to be required for the effect of the hormone on the regulation of metabolism (19 -21) and on gene expression (43). Moreover, the K ϩ uptake may confer support for cell survival (7,8,16,46,48). To the extent that KCNQ1 counteracts the stimulation of cellular K ϩ uptake by insulin, the channel may blunt insulin sensitivity.…”

Hemin-induced suicidal erythrocyte death

“…Some of these diseases may cause eryptosis by stimulating the formation of hemin. Furthermore, several eryptosis-triggering xenobiotics and endogeneous substances have been identified, such as cordycepin [50], methylglyoxal [54], amyloid peptides [53], lipopetides [71] retinoic acid [55], paclitaxel [44], amantadine [23], chlorpromazine [1], ciglitazone [58], cyclosporine [56], Bay-5884 [65], curcumin [4], valinomycin [64], listeriolysin [25], aluminum [57], copper [46], bismuth [13], tin [52], cadmium [68], selenium [67], vanadate [27], gold [69], and arsenic [51]. At least in theory, some of those substances may be effective through stimulation of hemin formation.…”