Cell death-inducing function and activation mechanism of Cl- channel

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Cell acidosis may induce the necrotic cell volume increase (NVI) due to NaCl accumulation within the cells by stimulation of Na+-H+ antiporter and C1--HC03- antiporter. Acidosis with lactate accumulation due to augmented glycolysis-fermentation reactions is known to be frequently associated with cerebral ischemia or trauma and to result in necrosis of glial and neuronal cells. Under such conditions called lactacidosis, cell swelling is strengthened by entry of lactate and proton via monocarboxylate transporters. In cultured glial C6 cells, persistent swelling was in fact induced by lactacidosis. Furthermore, the succeeding regulatory volume decrease (RVD) was impaired under lactacidosis conditions due to inhibition on volume-sensitive outwardly rectifying (VSOR) Cl- channels. When lactacidosis-resistant anion channels were exogenously introduced by applying an anion channel-forming toxin protein purified from Helicobacter pylori, VacA, glial cells restored the RVD. Furthermore, lactaci … More dosis-induced necrotic cell death was significantly rescued, when lactacidosis-resistant anion channels were exogenously introduced into C6 cells by pretreatment with the VacA protein. Thus, it is concluded that inhibition of volume-regulatory VSOR Cl- channels are involved in the NVI in glial cells.Apoptotic volume decrease (AVD) is a pivotal event triggering a cell to undergo apoptosis and is induced by ionic effluxes resulting mainly from increased K+ and Cl- conductances. In human epithelia HeLa cells both mitochondrion- and death receptor-mediated apoptosis inducers (staurosporine and Fas ligand or TNFα) rapidly activate Cl- currents that show properties phenotypical of VSOR Cl- channel currents. Staurosporine rapidly increased the intracellular level of reactive oxygen species (ROS). A ROS scavenger and an NAD(P)H oxidase inhibitor blocked the current activation by staurosporine. A ROS scavenger also inhibited AVD, caspase-3 activation and apoptotic cell death induced by staurosporine. Thus, it is concluded that an apoptosis-triggering anion conductance is carried by the VSOR Cl- channel and that the channel activation upon apoptotic stimulation with staurosporine is mediated by reactive oxygen species.Cultured mouse cortical neurons express the volume-sensitive outwardly rectifying (VSOR) anion channel. Under excitotoxic conditions, neurons suffered from pathological swelling and dendritic beading, called varicosity, and thereafter necrosis. Both whole-cell and single-channel recordings confirmed that the VSOR channel was activated by excitotoxicity. When a VSOR channel blocker was applied during exctitotoxic stimulation, varicosity formation and necrotic cell death were largely inhibited. Thus, it is concluded that the VSOR channel plays a role in excitotoxicity-induced varicosity formation and necrotic cell death. Less