title: Acacetin causes a frequency- and use-dependent blockade of hKv1.5 channels by binding to the S6 domain.
abstract: We have demonstrated that the natural flavone acacetin selectively inhibits ultra-rapid delayed rectifier potassium current (I(Kur)) in human atria. However, molecular determinants of this ion channel blocker are unknown. The present study was designed to investigate the molecular determinants underlying the ability of acacetin to block hKv1.5 channels (coding I(Kur)) in human atrial myocytes using the whole-cell patch voltage-clamp technique to record membrane current in HEK 293 cells stably expressing the hKv1.5 gene or transiently expressing mutant hKv1.5 genes generated by site-directed mutagenesis. It was found that acacetin blocked hKv1.5 channels by binding to both closed and open channels. The blockade of hKv1.5 channels by acacetin was use- and frequency-dependent, and the IC(50) of acacetin for inhibiting hKv1.5 was 3.5, 3.1, 2.9, 2.1, and 1.7μM, respectively, at 0.2, 0.5, 1, 3, and 4Hz. The mutagenesis study showed that the hKv1.5 mutants V505A, I508A, and V512A in the S6-segment remarkably reduced the channel blocking properties by acacetin (IC(50), 29.5μM for V505A, 19.1μM for I508A, and 6.9μM for V512A). These results demonstrate the novel information that acacetin mainly blocks open hKv1.5 channels by binding to their S6 domain. The use- and rate-dependent blocking of hKv1.5 by acacetin is beneficial for anti-atrial fibrillation.
authors: Department and Medicine, Li Ka Shing Faculty of Medicine, the University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors: Hui-Jun
authors: HJ
authors: Wu
authors: Wei
authors: W
authors: Wu
authors: Hai-Ying
authors: HY
authors: Sun
authors: Guo-Wei
authors: GW
authors: Qin
authors: Hong-Bing
authors: HB
authors: Wang
authors: Panwen
authors: P
authors: Wang
authors: Hari Krishna
authors: HK
authors: Yalamanchili
authors: Junwen
authors: J
authors: Wang
authors: Hung-Fat
authors: HF
authors: Tse
authors: Chu-Pak
authors: CP
authors: Lau
authors: Paul M
authors: PM
authors: Vanhoutte
authors: Gui-Rong
authors: GR
authors: Li
mesh_terms: D019943:Amino Acid Substitution; D002460:Cell Line; D047309:Flavones / Q000378:metabolism / Q000494:pharmacology*; D057809:HEK293 Cells; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051666:Kv1.5 Potassium Channel / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D008564:Membrane Potentials; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics
chemical_list: D047309:Flavones; D051666:Kv1.5 Potassium Channel; D026902:Potassium Channel Blockers; C023717:acacetin