Impaired endothelium-derived hyperpolarizing factor-mediated dilations and increased blood pressure in mice deficient of the intermediate-conductance Ca2+-activated K+ channel

The endothelium plays a key role in the control of vascular tone and alteration in endothelial cell function contributes to several cardiovascular disease states. Endothelium-dependent dilation is mediated by NO, prostacyclin, and an endothelium-derived hyperpolarizing factor ( EDHF). EDHF signaling is thought to be initiated by activation of endothelial Ca2+-activated K+ channels (K-Ca), leading to hyperpolarization of the endothelium and subsequently to hyperpolarization and relaxation of vascular smooth muscle. In the present study, we tested the functional role of the endothelial intermediate-conductance K-Ca (IKCa/K(Ca)3.1) in endothelial hyperpolarization, in EDHF-mediated dilation, and in the control of arterial pressure by targeted deletion of K(Ca)3.1. K(Ca)3.1-deficient mice (K(Ca)3.1(-/-)) were generated by conventional gene-targeting strategies. Endothelial KCa currents and EDHF-mediated dilations were characterized by patch-clamp analysis, myography and intravital microscopy. Disruption of the KCa3.1 gene abolished endothelial KCa3.1 currents and significantly diminished overall current through KCa channels. As a consequence, endothelial and smooth muscle hyperpolarization in response to acetylcholine was reduced in K(Ca)3.1(-/-) mice. Acetylcholine-induced dilations were impaired in the carotid artery and in resistance vessels because of a substantial reduction of EDHF-mediated dilation in KCa3.1(-/-) mice. Moreover, the loss of KCa3.1 led to a significant increase in arterial blood pressure and to mild left ventricular hypertrophy. These results indicate that the endothelial KCa3.1 is a fundamental determinant of endothelial hyperpolarization and EDHF signaling and, thereby, a crucial determinant in the control of vascular tone and overall circulatory regulation.