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DOI: 10.1055/s-2007-990246
© Georg Thieme Verlag KG Stuttgart · New York
Large Conductance Ca2+-Activated K+ (BKCa) Channels are Involved in the Vascular Relaxations Elicited by Piceatannol Isolated from Rheum undulatum rhizome
Publikationsverlauf
Received: July 27, 2007
Revised: September 19, 2007
Accepted: September 21, 2007
Publikationsdatum:
24. Oktober 2007 (online)
![](https://www.thieme-connect.de/media/plantamedica/200714/lookinside/thumbnails/10.1055-s-2007-990246-1.jpg)
Abstract
We previously reported that piceatannol isolated from the rhizome extract of Rheum undulatum has a potent vasorelaxant activity. In the present study, the mechanisms underlying the direct vascular relaxant effect of piceatannol were investigated in isolated rat aorta. Piceatannol induced a concentration-dependent relaxation in aortic preparations precontracted with phenylephrine (EC50 : 2.4 ± 0.4 μM), which was completely inhibited by endothelial removal, N ω-nitro-L-arginine (nitric oxide synthase inhibitor), methylene blue and 1H-[1] [2] [4]oxadiazolo [4,3-a]quinoxalin-1-one (guanylyl cyclase inhibitor). The piceatannol-induced relaxation was also blocked by raising the extracellular K+ (45 mM), 4-aminopyridine (voltage-sensitive K+ channel blocker) and tetraethylammonium [the non-selective Ca2+-activated K+ (KCa) channel blocker] but not by indomethacin (cyclooxygenase inhibitor), atropine (muscarinic receptor antagonist), propranolol (β-adrenoceptor antagonist), verapamil and nifedipine (L-type voltage-gated Ca2+ channel blocker), barium chloride (inward rectifier K+ channel inhibitor) and glibenclamide (ATP-sensitive K+ channel blocker). In further studies investigating the role of Ca2+-activated K+ (KCa) channels, piceatannol-induced relaxant responses were decreased by charybdotoxin [large (BKCa)- and intermediate (IKCa)-conductance KCa channel blocker], iberiotoxin (selective BKCa channels blocker), but not by apamin [small-conductance KCa (SKCa) channel blocker], TRAM-34 [intermediate-conductance KCa (IKCa) channel blocker]. The present results demonstrate that piceatannol-induced vascular relaxation in rat aorta may be mediated by an endothelium-dependent nitric oxide signaling pathway, at least partially, through the activation of BKCa.
Abbreviations
BKCa channel: large conductance KCa channel
IKCa channel: intermediate conductance KCa channel
KATP channel: ATP-sensitive K+ channel
KCa channel: Ca2+-activated K+ channel
KIR channel: inward rectifier K+ channel
Kv channel: voltage-dependent K+ channel
L-NNA: N ω-nitro-L-arginine
MB: methylene blue
ODQ: 1H-[1] [2] [4] oxadiazolo[4,3-a]quinoxalin-1-one
SKCa channel: small conductance KCa channel
TEA: tetraethylammonium
TRAM 34: 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole
Key words
Rheum undulatum - Polygonaceae - piceatannol - vasorelaxation - Ca2+-activated K+ channel - BKCa channels - rat aorta
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Byung Ho Lee, PhD
Drug Discovery Division
Korea Research Institute of Chemical Technology
100 Jang-dong
Yuseong
Daejeon 305-343
Republic of Korea
Telefon: +82-42-860-7415
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