Involvement of mitochondrial K⁺ release and cellular efflux in ischemic and apoptotic neuronal death

We measured and manipulated intracellular potassium (K⁺) fluxes in cultured hippocampal neurons in an effort to understand the involvement of K⁺ in neuronal death under conditions of ischemia and exposure to apoptotic stimuli Measurements of the intracellular K⁺ concentration using the fluorescent probe 1,3-benzenedicarboxylic acid, 4,4′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7, 16-diyl-bis(5-methoxy-6,2-benzofurandiyl)]bis-, tetrakis [(acetyloxy) methyl] ester (PBFI) revealed that exposure of neurons to cyanide (chemical hypoxia), glutamate (excitotoxic insult) or staurosporine (apoptotic stimulus) results in efflux of K⁺ and cell death. Treatment of neurons with 5-hydroxydecanoate (5HD), an inhibitor of mitochondrial K⁺ channels, reduced K⁺ fluxes in neurons exposed to each insult and increased the resistance of the cells to death. K⁺ efflux was attenuated, levels of oxyradicals were decreased, mitochondrial membrane potential was stabilized and release of cytochrome c from mitochondria was 3 attenuated in neurons treated with 5HD. K⁺ was rapidly released into the cytosol from mitochondria when neurons were exposed to the K⁺ channel opener, diazoxide, or to the mitochondrial uncoupler, carbonyl cyanide 4(trifluoromethoxy)-phenylhydrazone (FCCP), demonstrating that the intramitochondrial K⁺ concentration is greater than the cytosolic K⁺ concentration. The release of K⁺ from mitochondria was followed by efflux through plasma membrane K⁺ channels. In vivo studies showed that 5HD reduces ischemic brain damage without affecting cerebral blood flow in a mouse model of focal ischemic stroke. These findings suggest that intracellular K⁺ fluxes play a key role in modulating neuronal oxyradical production and cell survival under ischemic conditions, and that agents that modify K⁺ fluxes may have therapeutic benefit in stroke and related neurodegenerative conditions.