Hydrogen peroxide, potassium currents, and membrane potential in human endothelial cells

Background-Hydrogen peroxide (H2O2) and reactive oxygen species are implica ted in inflammation, ischemia-reperfusion injury, and atherosclerosis. The role of ion channels has not been previously explored. Methods and Results-K+ currents and membrane potential were recorded in end othelial cells by voltage- and current-clamp techniques. H2O2 elicited both hyperpolarization and depolarization of the membrane potential in a concen tration-dependent manner. Low H2O2 concentrations (0.01 to 0.25 mu mol/L) i nhibited the inward-rectifying K+ current (K-IR) Whole-cell K+ current anal ysis revealed that H2O2 (1 mmol/L) applied to the bath solution increased t he Ca2+-dependent K+ current (K-Ca) amplitude. H2O2 increased K-Ca current in outside-out patches in a Ca2+-free solution. When catalase (5000 mu/mL) was added to the bath solution, the outward-rectifying K+ current amplitude was restored. In contrast, superoxide dismutase (1000 u/mL) had only a sma ll effect on the H2O2-induced K+ current changes. Next, we measured whole-c ell K+ currents and redox potentials simultaneously with a novel redox pote ntial-sensitive electrode. The H2O2-mediated K-Ca current increase was acco mpanied by a whole-cell redox potential decrease. Conclusions-H2O2 elicited both hyperpolarization and depolarization of the membrane potential through 2 different mechanisms. Low H2O2 concentrations inhibited inward-rectifying K+ currents, whereas higher H2O2 concentrations increased the amplitude of the outward K+ current. We suggest that reactiv e oxygen species generated locally increases the K-Ca current amplitude, wh ereas low H2O2 concentrations inhibit K-IR via intracellular messengers.