Endothelial SK3 channel-associated Ca2+ microdomains modulate blood pressure

摘要

Activation of vascular endothelial small- (KCa2.3, SK3) or intermediate- (KCa3.1, IK1) conductance Ca²⁺-activated potassium channels induces vasorelaxation via an endothelium-derived hyperpolarization (EDH) pathway. Although the activation of SK3 and IK1 channels converges on EDH, their subcellular effects on signal transduction are different and not completely clear. In this study, a novel endothelium-specific SK3 knockout (SK3^−/−) mouse model was utilized to specifically examine the contribution of SK3 channels to mesenteric artery vasorelaxation, endothelial Ca²⁺ dynamics, and blood pressure. The absence of SK3 expression was confirmed using real-time quantitative PCR and Western blot analysis. Functional studies showed impaired EDH-mediated vasorelaxation in SK3^−/− small mesenteric arteries. Immunostaining results from SK3^−/− vessels confirmed the absence of SK3 and further showed altered distribution of transient receptor potential channels, type 4 (TRPV4). Electrophysiological recordings showed a lack of SK3 channel activity, while TRPV4-IK1 channel coupling remained intact in SK3^−/− endothelial cells. Moreover, Ca²⁺ imaging studies in SK3^−/− endothelium showed increased Ca²⁺ transients with reduced amplitude and duration under basal conditions. Importantly, SK3^−/− endothelium lacked a distinct type of Ca²⁺ dynamic that is sensitive to TRPV4 activation. Blood pressure measurements showed that the SK3^−/− mice were hypertensive, and the blood pressure increase was further enhanced during the 12-h dark cycle when animals are most active. Taken together, our results reveal a previously unappreciated SK3 signaling microdomain that modulates endothelial Ca²⁺ dynamics, vascular tone, and blood pressure.