Abstract-Inwardly rectifying Kϩ (Kir) channels are responsible for maintaining endothelial membrane potential and play a key role in endothelium-dependent vasorelaxation. In this study, we show that endothelial Kir channels are suppressed by hypercholesterolemic levels of lipoproteins in vitro and by serum hypercholesterolemia in vivo. Specifically, exposing human aortic endothelial cells to acetylated low-density lipoprotein or very low density lipoprotein resulted in a time-and concentration-dependent decrease in Kir current that correlated with the degree of cholesterol loading. The suppression was fully reversible by cholesterol depletion. Furthermore, a decrease in Kir current resulted in depolarization of endothelial membrane potential. Most important, the flow sensitivity of Kir currents was also impaired by cholesterol loading. Specifically, flow-induced increase in Kir current was suppressed by 70%, and flow-induced hyperpolarization was almost completely abrogated. Furthermore, we show that hypercholesterolemia in vivo also strongly suppresses endothelial Kir currents and causes a shift in endothelial membrane potential, as determined by comparing the currents in aortic endothelial cells freshly isolated from healthy or hypercholesterolemic pigs. Therefore, we suggest that suppression of Kir current is one of the important factors in hypercholesterolemia-induced endothelial dysfunction. (Circ Res. 2006;98:1064-1071.) Key Words: K channels Ⅲ cholesterol Ⅲ lipoproteins Ⅲ flow Ⅲ vasodilatation N umerous studies have shown that a major risk factor for the development of cardiovascular disease is plasma hypercholesterolemia, elevation of low-and very low-density lipoproteins (LDL and VLDL), as well as the oxidized modification of LDL, oxidized LDL (oxLDL). 1,2 Endothelial dysfunction develops in the early stages of cardiovascular disease and is a strong predictor of its development. 3 A hallmark of endothelial dysfunction in vivo is impairment of flow-mediated vasodilatation (FMV). Indeed, several studies have shown that plasma hypercholesterolemia impairs FMV both in humans and in animal models of atherosclerosis. 4,5 However, molecular mechanisms that underlie hypercholesterolemia-induced endothelial dysfunction are poorly understood.Our studies focus on the impact of hypercholesterolemia on endothelial inwardly rectifying K ϩ (Kir) channels, the major determinants of endothelial membrane potential 6,7 and putative flow sensors. 8 -10 The resting membrane potential in endothelial cells ranges between approximately Ϫ30 and Ϫ80 mV depending on a specific endothelial cell type. 7 Aortic endothelial cells typically have resting potentials in a strongly hyperpolarizing range (approximately Ϫ60 mV/Ϫ80 mV) both in culture 8,[11][12][13] and in intact aortas, 14 consistent with a major contribution of K ϩ channels. Several types of K ϩ channels are expressed in endothelial cells: Kir channels that maintain stable membrane potential under resting condition and are responsible for flow-induced hyperpolarization an...

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