Voltage‐gated K⁺ current: a marker for apoptosis in differentiating neuronal progenitor cells?

Abstract

We investigated apoptosis during early stages of in vitro differentiation of neuronal precursors generated by embryonic day 14 (E14) mouse striata stem cells. Differentiation was in conditions of suboptimal growth factor supply. Apoptosis reached 10-15% of cells and affected proliferating as well as postmitotic cells, including TUJ1-positive cells. Inhibition of apoptosis led to an increased proportion of TUJ1-positive cells generated by stem cells. K(+) current was reported to be related to apoptosis. Outward K(+) currents were present in differentiating neuronal precursors that were consistent with delayed rectifier and transient A-type currents. The amplitude of the delayed rectifier current varied during the first 4 days of stem cell differentiation. Current amplitude was greatly increased in the presence of staurosporine but reduced at elevated extracellular K(+) concentration. In addition, the amplitude of the current was significantly diminished by inhibiting several caspases, but not caspase 8. In Bax knock-out transgenic neuronal precursors, K(+) current was not decreased after the first day but at later stages of cell differentiation. At this early stage, apoptosis of proliferating cells and of TUJ1-positive cells was not reduced by the absence of Bax, but was by caspase 9 inhibition. Thus, activation of a delayed rectifier K(+) current in differentiating stem cells is related to apoptosis. Recordings of this current revealed that apoptosis at early stages of neuronal differentiation occurred in two phases that did not exhibit similar dependence on the proapoptotic protein Bax and that probably used different pathways.

Inhibitory effect of ganglioside GD1b on K+ current in hippocampal neurons and its involvement in apoptosis suppression

“…4B, C). This result is consistent with previous reports that the apoptosis inducer STS greatly augmented I K (15,23). Application of 10 M GD1b inhibited the current by ‫%02ف‬ for both intracellular application of 0.1 nM and extracellular application of 10 nM STS (Fig.…”

“…Fourth, GD1b suppressed the caspase 3 activation induced by STS. Activation of the outward K ϩ current has been shown to be essential to apoptosis in almost all cell types (23). Thus, the first two lines of evidence suggest that GD1b may prevent the intracellular K ϩ loss and consequently suppress apoptosis.…”

Neural Stem and Progenitor Cells Retain Their Potential for Proliferation and Differentiation into Functional Neurons Despite Lower Number in Aged Brain

“…Ion channel composition also changed during differentiation (Hribar et al, 2004). We observed a decrease of K ϩ channel density in comparison with the proliferating stage but with no differences between age groups.…”

“…Since we observed lower cell survival in adult and aged groups, the latter observation could indicate higher predisposition of older cells to undergo apoptosis. Enhancement of plasma membrane permeability to K ϩ ions is known to be associated with apoptosis in various cell types (Bortner et al, 1997;Yu et al, 1997Yu et al, , 1999Hribar et al, 2004). Delayed rectified K ϩ current in proliferating embryonic NSCs cells and lack of A-type K ϩ current have been reported (Pagani et al, 2006).…”

Calcium- and Metabolic State-Dependent Modulation of the Voltage-Dependent Kv2.1 Channel Regulates Neuronal Excitability in Response to Ischemia

“…In cultured cortical neurons, increased TEA-sensitive I K in response to proapoptotic treatments (long-term serum deprivation or staurosporine treatment) is critical to the induction of apoptosis, such that TEA is antiapoptotic (Yu et al, 1997(Yu et al, , 1999bWang et al, 2000;Wei et al, 2003). Models linking I K -mediated K ϩ efflux to altered [K ϩ ] i homeostasis, cell shrinkage, and proapoptotic cytochrome c release from mitochondria, as well as to direct K ϩ regulation of caspase, have been proposed (Yu et al, 1999b;Wei et al, 2003;Hribar et al, 2004). Knockdown experiments in cultured cortical neurons revealed that Kv2.1 is the specific TEA-sensitive Kv channel underlying the proapoptotic I K activity (Pal et al, 2003).…”