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Apigenin‐induced nitric oxide production involves calcium‐activated potassium channels and is responsible for antiangiogenic effects
Author(s) -
ERDOGAN A.,
MOST A. K.,
WIENECKE B.,
FEHSECKE A.,
LECKBAND C.,
VOSS R.,
GREBE M. T.,
TILLMANNS H.,
SCHAEFER C. A.,
KUHLMANN C. R. W.
Publication year - 2007
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2007.02615.x
Subject(s) - iberiotoxin , chemistry , apamin , cyclic guanosine monophosphate , nitric oxide , protein kinase b , biochemistry , microbiology and biotechnology , signal transduction , calcium , biology , organic chemistry
Summary. Background: The dietary flavonoid apigenin (Api) has been demonstrated to exert multiple beneficial effects upon the vascular endothelium. The aim of this study was to examine whether Ca 2+ ‐activated K + channels (K Ca ) are involved in endothelial nitric oxide (NO) production and antiangiogenic effects. Methods: Endothelial NO generation was monitored using a cyclic guanosine monophosphate radioimmunoassay. K Ca activity and changes of the intracellular Ca 2+ concentration [Ca 2+ ] i were analyzed using the fluorescent dyes bis‐barbituric acid oxonol, potassium‐binding benzofuran isophthalate, and fluo‐3. The endothelial angiogenic parameters measured were cell proliferation, [ 3 H]‐thymidine incorporation, and cell migration (scratch assay). Akt phosphorylation was examined using immunohistochemistry. Results: Api caused a concentration‐dependent increase in cyclic guanosine monophosphate levels, with a maximum effect at a concentration of 1 μ m . Api‐induced hyperpolarization was blocked by the small and large conductance K Ca inhibitors apamin and iberiotoxin, respectively. Furthermore, apamin and iberiotoxin blocked the late, long‐lasting plateau phase of the Api‐induced biphasic increase of [Ca 2+ ] i . Inhibition of Ca 2+ signaling and the K Ca blockade both blocked NO production. Prevention of all three (NO, Ca 2+ , and K Ca signaling) reversed the antiangiogenic effects of Api under both basal and basic fibroblast growth factor‐induced culture conditions. Basic fibroblast growth factor‐induced Akt phosphorylation was also reduced by Api. Conclusions: Based on our experimental results we propose the following signaling cascade for the effects of Api on endothelial cell signaling. Api activates small and large conductance K Ca , leading to a hyperpolarization that is followed by a Ca 2+ influx. The increase of [Ca 2+ ] i is responsible for an increased NO production that mediates the antiangiogenic effects of Api via Akt dephosphorylation.