Ca2+-activated K+ channels of small and intermediate conductance control eNOS activation through NAD(P)H oxidase
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Date
2012
Journal Title
Journal ISSN
Volume Title
Publisher
ELSEVIER SCIENCE INC
Abstract
Ca2+-activated K+ channels (K-Ca) and NO play a central role in the endothelium-dependent control of vasomotor tone. We evaluated the interaction of K-Ca with NO production in isolated arterial mesenteric beds of the rat. In phenylephrine-contracted mesenteries, acetylcholine (ACh)-induced vasodilation was reduced by NO synthase (NOS) inhibition with N-omega-nitro-L-arginine (L-NA), but in the presence of tetraethylammonium, L-NA did not further affect the response. In KCl-contracted mesenteries, the relaxation elicited by 100 nM ACh or 1 mu M ionomycin was abolished by L-NA, tetraethylammonium, or simultaneous blockade of small-conductance K-Ca (SKCa) channels with apamin and intermediate-conductance K-Ca (IKCa) channels with triarylmethane-34 (TRAM-34). Apamin-TRAM-34 treatment also abolished 100 nM ACh-activated NO production, which was associated with an increase in superoxide formation. Endothelial cell Ca2+ buffering with BAPTA elicited a similar increment in superoxide. Apamin-TRAM-34 treatment increased endothelial NOS phosphorylation at threonine 495 (P-eNOS(Thr495)). Blockade of NAD(P)H oxidase with apocynin or superoxide dismutation with PEG-SOD prevented the increment in superoxide and changes in P-eNOS(Thr495) observed during apamin and TRAM-34 application. Our results indicate that blockade of SKCa and IKCa activates NAD(P)H oxidase-dependent superoxide formation, which leads to inhibition of NO release through P-eNOS(Thr495). These findings disclose a novel mechanism involved in the control of NO production. (C) 2011 Elsevier Inc. All rights reserved.
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Keywords
Endothelial cells, Nitric oxide production, NAD(P)H oxidase, Superoxide formation, eNOS phosphorylation, Vasodilation, Free radicals, ENDOTHELIUM-DEPENDENT HYPERPOLARIZATION, ACETYLCHOLINE-INDUCED VASODILATION, RECTIFYING POTASSIUM CHANNELS, RAT MESENTERIC-ARTERIES, NITRIC-OXIDE, GAP-JUNCTIONS, MEDIATED RESPONSES, VASCULAR FUNCTION, BLOOD-PRESSURE, CELLS