Differential oxidative modulation of voltage-dependent K+ currents in rat hippocampal neurons

Oxidative stress is enhanced by [Ca2+]i-dependent stimulation of phospholipases and mitochondria and has been implicated in immune defense, ischemia, and excitotoxicity. Using whole cell recording from hippocampal neurons, we show that arachidonic acid (AA) and hydrogen peroxide (H2O2) both reduce the transient K+ current I(A) by -54 and -68%, respectively, and shift steady-state inactivation by -10 and -15 mV, respectively. While AA was effective at an extracellular concentration of 1 microM and an intracellular concentration of 1 pM, extracellular H2O2 was equally effective only at a concentration >800 microM (0.0027%). In contrast to AA, H2O2 decreased the slope of activation and increased the slope of inactivation of I(A) and reduced the sustained delayed rectifier current I(K(V)) by 22% and shifted its activation by -9 mV. Intracellular application of the antioxidant glutathione (GSH, 2-5 mM) blocked all effects of AA and the reduction of I(A) by H2O2. In contrast, intracellular GSH enhanced reduction of I(K(V)) by H2O2. Decrease of the slope of activation and increase of the slope of inactivation of I(A) by hydrogen peroxide was blocked and reversed to a decrease, respectively, by intracellular application of GSH. Intracellular GSH did not prevent H2O2 to shift inactivation and activation of I(A) and activation of I(K(V)) to more negative potentials. We conclude, that AA and H2O2 modulate voltage-activated K currents differentially by oxidation of GSH accessible intracellular and GSH inaccessible extracellular K+-channel domains, thereby presumably affecting neuronal information processing and oxidative damage.