Activation of iberiotoxin-sensitive, Ca2+-activated K+ channels of porcine isolated left anterior descending coronary artery by diosgenin.
The objective of this study was to determine the vasodilating effect of 3beta-hydroxy-5-spirostene (diosgenin), a phytoestrogen found in wild yams, using porcine resistance left anterior descending coronary artery. In 5-hydroxytryptamine (3 microM) pre-contracted preparation, diosgenin caused a concentration-dependent (0.01 to 1 microM), endothelium-independent relaxation, with a maximum relaxation of approximately 72% at 1 microM. No apparent effect was observed with 17beta-oestradiol and progesterone with concentrations < or =0.3 microM, and a relaxation of approximately 15% and approximately 23% caused by 17beta-oestradiol (1 microM) and progesterone (1 microM), respectively. Diosgenin-elicited relaxation was not altered by 7alpha,17beta-[9[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol (ICI 182,780), mifepristone, (+)-bicuculline, cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL 12330A), glibenclamide and scavengers of reactive oxygen species. The iberiotoxin-sensitive, Ca2+-activated K+ (BK(Ca)) current of single vascular myocytes recorded, using patch-clamp techniques, was markedly enhanced by diosgenin, 17beta-oestradiol and progesterone. Application of (9S, 10R, 12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylic acid methyl ester (KT 5823, 300 nM) eradicated the enhancement of BK(Ca) amplitude. Diosgenin, 17beta-oestradiol and progesterone did not affect whereas phloretin, biochanin A and zearalanone (1 microM each) significantly suppressed [Ca2+]o-induced contraction. In oestrogen competition essay using human breast cancer cell (MCF-7 cells), diosgenin (0.001 nM to 10 microM) did not interact with oestrogen receptor-alpha, and no displacement of [3H]17beta-oestradiol was observed. In oestrogen receptor alpha- and beta-fluorescence polarization competitor assay, diosgenin (100 microM) demonstrated a greater competition with the beta-isoform of oestrogen receptor. These results suggest that diosgenin caused an acute, endothelium-independent coronary artery relaxation via protein kinase G signalling cascade and an activation of BK(Ca) channel of arterial smooth muscle cells. The oestrogen receptor (alpha and beta-isoforms) and progesterone receptor are probably not involved.
Room 409B, Basic Medical Sciences Building, Department of Pharmacology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, PR China.
Alice Lai Shan
AL
Au
Ching Chi
CC
Kwok
Allen Ting Chun
AT
Lee
Yiu Wa
YW
Kwan
Macey Mei Sze
MM
Lee
Rong-Zhen
RZ
Zhang
Sai Ming
SM
Ngai
Simon Ming Yuen
SM
Lee
Guo-Wei
GW
He
Kwok Pui
KP
Fung
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004144:Diosgenin / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D010455:Peptides / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D010455:Peptides; D024681:Potassium Channels, Calcium-Activated; C064719:iberiotoxin; D004144:Diosgenin