Hydrogen peroxide increases cerebral arterial KCa channel opening through activation of Akt signaling pathway

Abstract

The oxidant hydrogen peroxide (H2O2) is not only an inducer of cellular damage, but can also play a role as a modulator of vascular function. Exogenous application of H2O2 (3‐300 µM) resulted in a concentration‐dependent increase in NPo of KCa single‐channel currents recorded from cell attached patches at a patch potential of +40 mV, whereas this oxidant did not change the NPo of KCa single‐channel current when recorded from excised inside‐out membrane patches of cerebral arterial muscle cells (CAMCs). The membrane permeant organic peroxide tert‐butyl hydroperoxide (t‐BOOH) (30 µM) also induced similar increase in NPo of KCa single‐channel currents in the cell‐attached patches but had no effect on NPo of the single‐channel KCa currents recorded from excised inside‐out patches at a the same patch potential. In an attempt to elucidate possible signaling mechanism mediating the effects of these oxidants on KCa channel currents in CAMCs, we examined the impact of inhibition of the phospoinositide 3‐kinase‐Akt (PI3K‐Akt) pathway on the stimulatory actions of both H2O2 and t‐BOOH on KCa channel current. Pretreatment of CAMCs with two structurally different PI3K‐Akt pathway inhibitors wortmannin (10 nM) and LY294002 (5 µM) significantly attenuated the H2O2‐ or t‐BOOH‐induced increase in NPo of single‐channel KCa currents in CAMCs. On the other hand, stimulation of cerebral arterial muscle with either H2O2 or t‐BOOH for 10 minutes induced activation of Akt as determined by western blot analysis. These findings suggest that activation of the Akt signaling pathway contributes to the H2O2‐or t‐BOOH‐induced enhancement of KCa channel currents in cerebral arterial muscle cells.