Improvement of endothelium-dependent vasodilations by SKA-31 and SKA-20, activators of small- and intermediate-conductance Ca2+-activated K+-channels

Aim: Endothelial membrane hyperpolarization mediated by KCa3.1 and KCa2.3 channels has been demonstrated to initiate endothelium-derived hyperpolarizing factor (EDHF)-type vasodilations. Moreover, pharmacological potentiation of KCa3.1/KCa2.3 channels has been suggested to improve EDHF-type vasodilations. Herein, we determined whether the KCa3.1/KCa2.3 activator SKA-31 and its derivative SKA-20 improve endothelial dysfunction in KCa3.1-/- and NOS3-/- mice. Methods: Membrane potentials were measured using patch-clamp electrophysiology on carotid artery (CA) endothelial cells (CAEC) from wild-type (wt) and KCa3.1-/- mice. Endothelium-dependent vasodilations were determined by pressure myography in CA. Results: SKA-31 (1 mu M) activated KCa3.1 and KCa2.3 channels and induced membrane hyperpolarization in CAEC of wt (Delta MP -45 mV). These responses were significantly reduced in CAEC of KCa3.1-/- (Delta MP -8 mV). SKA-31 (200 nM, 500 nM) and SKA-20 (300 nM) significantly enhanced EDHF vasodilations in wt. SKA-20 also improved vasodilations during NO synthesis. In KCa3.1-/-, the defective EDHF vasodilations were unchanged at 200 nM SKA-31, but were significantly improved at 500 nM. EDHF vasodilations were slightly enhanced at 300 nM SKA-20, but vasodilations during NO synthesis were unchanged. SKA-31 (500 nM) enhanced the impaired endothelium-dependent vasodilation in NOS3-/- mice twofold. Pharmacological inhibition of the soluble epoxide hydrolase by t-AUCB (1 mu M) in contrast did not increase ACh-induced EDHF- or NO-mediated vasodilations in wt and KCa3.1-/-. Conclusion: Normal and defective endothelium-dependent vasodilations in murine carotid arteries can be improved by pharmacological enhancement of KCa3.1/KCa2.3 functions. These findings further support the concept that pharmacological activation of endothelial KCa2.3/KCa3.1 could offer a novel endothelium-specific antihypertensive strategy.