title: Ca2+ channel blocking effect of iso-S-petasin in rat aortic smooth muscle cells.
abstract: The purpose of the present study was to examine the mechanisms underlying the putative hypotensive actions of iso-S-petasin, a sesquiterpene extract of Petasites formosanus through both in vivo and in vitro experiments. Intravenous administration of iso-S-petasin elicited dose-dependent (0.1-1.5 mg/kg) hypotensive and bradycardiac responses in anesthetized rats. Isometric tension recording in isolated thoracic aorta revealed that iso-S-petasin (0.01-100 microM) inhibited KCl- or Bay K 8644 (1,4-dihydro-2,6-dimethyl-5-nitro-4-[2'-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid methyl ester)-induced vasoconstriction independent of endothelium. Iso-S-Petasin also attenuated Ca(2+)-induced vasoconstriction in a concentration-dependent manner in Ca(2+)-depleted/high K(+)-depolarized ring segments, indicating that iso-S-petasin inhibited Ca(2+) influx into vascular smooth muscle cells. This was confirmed by whole-cell patch-clamp recording in cultured vascular smooth muscle cells where iso-S-petasin (10-100 microM) appeared to directly inhibit the L-type voltage-dependent Ca(2+) channel (VDCC) activity. Intracellular Ca(2+) concentration ([Ca(2+)](i)) measurements using the fluorescent probe fura-2/AM (1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2'-amino-5'-methylphenoxy)-ethane-N,N,N',N'-tetraacetic acid pentaacetoxymethyl ester) showed suppression of the KCl-stimulated increase in [Ca(2+)](i) by iso-S-petasin (10, 100 microM). In conclusion, these results suggest that Ca(2+) antagonism of the L-type VDCC in vascular smooth muscle cells might largely account for the hypotensive action of iso-S-petasin.
authors.affiliation: National Research Institute of Chinese Medicine, Room 355, 155-1, Section 2, Li-Nong Street, Pei-tou District (112), Taipei, Taiwan, ROC. jennyw@cma23.nricm.edu.tw
authors.forename: Guei-Jane
authors.initials: GJ
authors.lastname: Wang
authors.forename: Xi-Chen
authors.initials: XC
authors.lastname: Wu
authors.forename: Yun-Lian
authors.initials: YL
authors.lastname: Lin
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
authors.forename: Andrew Yau-Chik
authors.initials: AY
authors.lastname: Shum
authors.forename: Yu-Yuan
authors.initials: YY
authors.lastname: Wu
authors.forename: Chieh-Fu
authors.initials: CF
authors.lastname: Chen
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D036901:Petasites / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012717:Sesquiterpenes / Q000737:chemistry / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010936:Plant Extracts; D012717:Sesquiterpenes; C418727:petasin