title: Frequency- and state-dependent blockade of human ether-a-go-go-related gene K+ channel by arecoline hydrobromide.
abstract: BACKGROUND
  The rapidly activating delayed rectifier potassium current (I(Kr)), whose pore-forming alpha subunit is encoded by the human ether-a-go-go-related gene (hERG), is a key contributor to the third phase of action potential repolarization. The aim of this study was to investigate the effect and mechanism of arecoline hydrobromide induced inhibition of hERG K(+) current (I(hERG)).
  
  
  METHODS
  Transient transfection of hERG channel cDNA plasmid pcDNA3.1 into the cultured HEK293 cells was performed using Lipofectamine. A standard whole-cell patch-clamp technique was used to record the I(hERG) before and after the exposure to arecoline.
  
  
  RESULTS
  Arecoline decreased the amplitude and the density of the I(hERG) in a concentration-dependent manner (IC(50) = 9.55 mmol/L). At test potential of +60 mV, the magnitude of I(hERG) tail at test pulse of -40 mV was reduced from (151.7 ± 6.2) pA/pF to (84.4 ± 7.6) pA/pF (P < 0.01, n = 20) and the magnitude of I(hERG) tail at test pulse of -110 mV was reduced from (-187.5 ± 9.8) pA/pF to (-97.6 ± 12.6) pA/pF (P < 0.01, n = 20). The blockade of arecoline in the open and inactivated state was significant in a state-dependent manner. The maximal blockade was achieved in the inactivated state. Studies of gating mechanism showed that the steady-state activation curve of I(hERG) was significantly negatively shifted by arecoline. Time constants of activation were shortened. Steady-state inactivation curve and time constants of fast inactivation were not significantly affected by arecoline. Furthermore, the inhibition of I(hERG) by arecoline was characterized markedly by a frequency-dependent manner from 0.03 to 1.00 Hz pulse.
  
  
  CONCLUSIONS
  Arecoline could potently block I(hERG) in both frequency and state-dependent manner.
authors.affiliation: Institute of Geriatric Cardiology, Chinese People's Liberation Army General Hospital, Beijing 100853, China.
authors.forename: Xu-yan
authors.initials: XY
authors.lastname: Zhao
authors.forename: Yu-qi
authors.initials: YQ
authors.lastname: Liu
authors.forename: Yi-cheng
authors.initials: YC
authors.lastname: Fu
authors.forename: Bin
authors.initials: B
authors.lastname: Xu
authors.forename: Jin-liao
authors.initials: JL
authors.lastname: Gao
authors.forename: Xiao-qin
authors.initials: XQ
authors.lastname: Zheng
authors.forename: Min
authors.initials: M
authors.lastname: Lin
authors.forename: Mei-yan
authors.initials: MY
authors.lastname: Chen
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D001115:Arecoline / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000037:antagonists & inhibitors* / Q000502:physiology; D057809:HEK293 Cells; D006801:Humans
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D001115:Arecoline