Oxidative stress induced by palmitic acid modulates KCa2.3 channels in vascular endothelium

Elevated plasma free fatty acids level has been implicated in the development of insulin resistance, inflammation, and endothelial dysfunction in diabetic and nondiabetic individuals. However, the underlying mechanisms still remain to be defined. Herein, we investigated the effect of palmitic acid (PA), the most abundant saturated fatty acid in the human body, on small-conductance Ca2+-activated potassium channels (K(Ca)2.3)-mediated relaxation in rodent resistance arteries and the underlying molecular mechanism. The effect of PA on K(Ca)2.3 in endothelium was evaluated using real-time PCR, Western blotting, whole-cell patch voltage-clamp, wire and pressure myograph system, and reactive oxygen species (ROS) were measured by using dihydroethidium and 2', 7'-dichlorofluorescein diacetate. K(Ca)2.3-mediated vasodilatation responses to acetylcholine and NS309 (agonist of K(Ca)2.3 and K(Ca)3.1) were impaired by incubation of normal mesenteric arteries with 100 mu M PA for 24 h. In cultured human umbilical vein endothelial cells (HUVECs), PA decreased K(Ca)2.3 current and expression at mRNA and protein levels. Incubation with the NADPH oxidase (Nox) inhibitor dibenziodolium (DPI) partly inhibited the PA-induced ROS production and restored K(Ca)2.3 expression. Inhibition of either p38-MAPK or NF-kappa B using specific inhibitors (SB203580, SB202190 or Bay11-7082, pyrrolidinedithiocarbamate) attenuated PA-induced downregulation of K(Ca)2.3 and inhibition of p38-MAPK also attenuated PA-induced phosphorylation of NF-kappa B p65. Furthermore, DPI reversed the increment of phospho-p38-MAPK by PA. These results demonstrated that PA downregulated K(Ca)2.3 expressions via Nox/ROS/p38-MAPK/NF-kappa B signaling leading to endothelial vasodilatory dysfunction.