Changes in intracellular electrolyte concentrations during apoptosis induced by UV irradiation of human myeloblastic cells

Abstract

Decreases in the intracellular concentrations of both K(+) and Cl(-) have been implicated in playing a major role in the progression of apoptosis, but little is known about the temporal relationship between decreases in electrolyte concentration and the key events in apoptosis, and there is no information about how such decreases affect different intracellular compartments. Electron probe X-ray microanalysis was used to determine changes in element concentrations (Na, P, Cl, and K) in nucleus, cytoplasm, and mitochondria in U937 cells undergoing UV-induced apoptosis. In all compartments, the initial stages of apoptosis were characterized by decreases in [K] and [Cl]. The largest decreases in these elements were in the mitochondria and occurred before the release of cytochrome c. Initial decreases in [K] and [Cl] also preceded apoptotic changes in the nucleus. In the later stages of apoptosis, the [K] continued to decrease, whereas that of Cl began to increase toward control levels and was accompanied by an increase in [Na]. In the nucleus, these increases coincided with poly(ADP-ribose) polymerase cleavage, chromatin condensation, and DNA laddering. The cytoplasm was the compartment least affected and the pattern of change of Cl was similar to those in other compartments, but the decrease in [K] was not significant until after active caspase-3 was detected. Our results support the concept that normotonic cell shrinkage occurs early in apoptosis, and demonstrate that changes in the intracellular concentrations of K and Cl precede apoptotic changes in the cell compartments studied.

Possible causes of apoptotic volume decrease: an attempt at quantitative review

“…Water measurement methods based on population analysis include gradient density centrifugation (5,127), NMR (108), quantification of intracellular markers (61,63), or drying and weighing (98). Microscopic approaches would require determination of the refractive index, which can be accomplished by quantitative phase microscopy (86); indeed, Model and Schonbrun (86) presented evidence that staurosporine and actinomycin D induce dehydration (AVD) as well as loss of dry mass.…”

“…Apparently, AVD can be an early (5,8,15,28,34,49,53,81) or a late (26,60,85,90,117) response, depending on the particular system. A few exceptions to the rule that AVD must accompany apoptosis have also been described (11,13,56,65,121,127); nevertheless, it appears that, in the vast majority of apoptotic models, AVD does occur sooner or later.…”

Cell shrinkage and monovalent cation fluxes: Role in apoptosis

“…Depending on the model system employed to study cell death, a late increase in intracellular sodium has also been reported during apoptosis. It was recently shown by x-ray microanalysis that staurosporine-induced [107] and UV-induced [108] apoptosis in U-937 cells resulted in an increase in intracellular sodium that occurs late in the cell death process. In these studies, the investigators could divide the changes in cellular elemental composition into two stages: an early stage characterized by a decrease in intracellular potassium concomitant with cell shrinkage and prior to caspase-3 activity or nuclear changes; and a later stage of decreased potassium content coupled with an increase in sodium content resulting from the activation of caspase-3.…”

The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

“…Several studies point out that it is not the specific ion per se that is involved in the apoptotic signaling, but rather a decrease in intracellular ionic strength (Arrebola et al, 2006(Arrebola et al, , 2005a(Arrebola et al, , 2005bHughes et al, 1997;Perez et al, 2000). Furthermore, increase in ionic strength has been shown to block the cytochrome c activated caspase-3 pathway (Hampton et al, 1998 (Ye et al, 2008).…”