title: Baicalin, a flavonoid from Scutellaria baicalensis Georgi, activates large-conductance Ca2+-activated K+ channels via cyclic nucleotide-dependent protein kinases in mesenteric artery.
abstract: Baicalin isolated from Scutellaria baicalensis is a traditional Chinese herbal medicine used for cardiovascular dysfunction. The ionic mechanism of the vasorelaxant effects of baicalin remains unclear. We investigated whether baicalin relaxes mesenteric arteries (MAs) via large-conductance Ca2+-activated K+ (BK(Ca)) channel activation and voltage-dependent Ca2+ channel (VDCC) inhibition. The contractility of MA was determined by dual wire myograph. BK(Ca) channels and VDCCs were measured using whole-cell recordings in single myocytes, enzymatically dispersed from rat MAs. Baicalin (10-100 microM) attenuated 80 mM KCl-contracted MA in a concentration-related manner. L-NAME (30 microM) and indomethacin (10 microM) little affected baicalin (100 microM)-induced vasorelaxations. Contractions induced by iberiotoxin (IbTX, 0.1 microM), Bay K8644 (0.1 microM) or PMA (10 microM) were abolished by baicalin 100 microM. In MA myocytes, baicalin (0.3-30 microM) enhanced BK(Ca) channel activity in a concentration-dependent manner. Increased BK(Ca) currents were abolished by IbTX (0.1 microM). Baicalin-mediated (30 microM) BK(Ca) current activation was significantly attenuated by an adenylate cyclase inhibitor (SQ 22536, 10 microM), a soluble guanylate cyclase inhibitor (ODQ, 10 microM), competitive antagonists of cAMP and cGMP (Rp-cAMP, 100 microM and Rp-cGMP, 100 microM), and cAMP- and cGMP-dependent protein kinase inhibitors (KT5720, 0.3 microM and KT5823, 0.3 microM). Perfusate with PMA (0.1 microM) abolished baicalin-enhanced BK(Ca) currents. Additionally, baicalin (0.3-30 microM) reduced the amplitude of VDCC currents in a concentration-dependent manner and abolished VDCC activator Bay K8644-enhanced (0.1 microM) currents. Baicalin produced MA relaxation by activating BK(Ca) and inhibiting VDCC channels by endothelium-independent mechanisms and by stimulating the cGMP/PKG and cAMP/PKA pathways.
authors.affiliation: Department of Pharmacology, College of Medicine, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan.
authors.forename: Yi-Ling
authors.initials: YL
authors.lastname: Lin
authors.forename: Zen-Kong
authors.initials: ZK
authors.lastname: Dai
authors.forename: Rong-Jyh
authors.initials: RJ
authors.lastname: Lin
authors.forename: Koung-Shing
authors.initials: KS
authors.lastname: Chu
authors.forename: Ing-Jun
authors.initials: IJ
authors.lastname: Chen
authors.forename: Jiunn-Ren
authors.initials: JR
authors.lastname: Wu
authors.forename: Bin-Nan
authors.initials: BN
authors.lastname: Wu
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D005260:Female; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000819:agonists*; D051381:Rats; D017207:Rats, Sprague-Dawley; D031364:Scutellaria baicalensis / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D024681:Potassium Channels, Calcium-Activated; C038044:baicalin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP