title: Kaempferol stimulates large conductance Ca2+ -activated K+ (BKCa) channels in human umbilical vein endothelial cells via a cAMP/PKA-dependent pathway.
abstract: OBJECTIVE
  Kaempferol has been shown to possess a vasodilator effect but its mechanism of action remains unclear. In this study, experiments were carried out to study the effect of kaempferol on K+ channels in endothelial cells.
  
  
  METHODS
  K+ channel activities in human umbilical vein endothelial cells (HUVECs) were studied by conventional whole cell and cell-attached patch-clamp electrophysiology.
  
  
  RESULTS
  Kaempferol stimulated an outward-rectifying current in HUVECs in a dose-dependent manner with an EC50 value of 2.5+/-0.02 microM. This kaempferol-induced current was abolished by large conductance Ca2+ -activated K+ (BKCa) channel blockers, such as iberiotoxin (IbTX) and charybdotoxin (ChTX), whereas the small conductance Ca2+ -activated K+ (SKCa) channel blocker, apamin, and the voltage-dependent K+ (KV) channel blocker, 4-aminopyridine, had no effect. Cell-attached patches demonstrated that kaempferol increased the open probability of BkCa channels in HUVECs. Clamping intracellular Ca2+ did not prevent kaempferol-induced increases in outward current. In addition, the kaempferol-induced current was diminished by the adenylyl cyclase inhibitor SQ22536, the cAMP antagonist Rp-8-Br-cAMP and the PKA inhibitor KT5720, but was not affected by the guanylyl cyclase inhibitor ODQ, the cGMP antagonist Rp-8-Br-cGMP and the PKG inhibitor KT5823. The activation of BKCa channels by kaempferol caused membrane hyperpolarization of HUVECs.
  
  
  CONCLUSIONS
  These results demonstrate that kaempferol activates the opening of BKCa channels in HUVECs via a cAMP/PKA-dependent pathway, resulting in membrane hyperpolarization. This mechanism may partly account for the vasodilator effects of kaempferol.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Y C
authors.initials: YC
authors.lastname: Xu
authors.forename: G P H
authors.initials: GP
authors.lastname: Leung
authors.forename: P Y D
authors.initials: PY
authors.lastname: Wong
authors.forename: P M
authors.initials: PM
authors.lastname: Vanhoutte
authors.forename: R Y K
authors.initials: RY
authors.lastname: Man
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000465:Algorithms; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004594:Electrophysiology; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D044949:Kaempferols / Q000494:pharmacology*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists*; D009126:Muscle Relaxation / Q000187:drug effects; D018408:Patch-Clamp Techniques; D015398:Signal Transduction / Q000187:drug effects*; D014471:Umbilical Veins / Q000166:cytology / Q000187:drug effects
chemical_list: D044949:Kaempferols; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015124:8-Bromo Cyclic Adenosine Monophosphate; C006552:kaempferol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases