title: H2O2-induced dilation in human coronary arterioles: role of protein kinase G dimerization and large-conductance Ca2+-activated K+ channel activation.
abstract: BACKGROUND
  Hydrogen peroxide (H(2)O(2)) serves as a key endothelium-derived hyperpolarizing factor mediating flow-induced dilation in human coronary arterioles (HCAs). The precise mechanisms by which H(2)O(2) elicits smooth muscle hyperpolarization are not well understood. An important mode of action of H(2)O(2) involves the oxidation of cysteine residues in its target proteins, including protein kinase G (PKG)-Iα, thereby modulating their activities.
  
  
  OBJECTIVE
  Here we hypothesize that H(2)O(2) dilates HCAs through direct oxidation and activation of PKG-Iα leading to the opening of the large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel and subsequent smooth muscle hyperpolarization.
  
  
  RESULTS
  Flow and H(2)O(2) induced pressure gradient/concentration-dependent vasodilation in isolated endothelium-intact and -denuded HCAs, respectively. The dilation was largely abolished by iberiotoxin, a BK(Ca) channel blocker. The PKG inhibitor Rp-8-Br-PET-cGMP also markedly inhibited flow- and H(2)O(2)-induced dilation, whereas the soluble guanylate cyclase inhibitor ODQ had no effect. Treatment of coronary smooth muscle cells (SMCs) with H(2)O(2) elicited dose-dependent, reversible dimerization of PKG-Iα, and induced its translocation to the plasma membrane. Patch-clamp analysis identified a paxilline-sensitive single-channel K(+) current with a unitary conductance of 246-pS in freshly isolated coronary SMCs. Addition of H(2)O(2) into the bath solution significantly increased the probability of BK(Ca) single-channel openings recorded from cell-attached patches, an effect that was blocked by the PKG-Iα inhibitor DT-2. H(2)O(2) exhibited an attenuated stimulatory effect on BK(Ca) channel open probability in inside-out membrane patches.
  
  
  CONCLUSIONS
  H(2)O(2) dilates HCAs through a novel mechanism involving protein dimerization and activation of PKG-Iα and subsequent opening of smooth muscle BK(Ca) channels.
authors.affiliation: Department of Medicine, Cardiovascular Center, Medical College of Wisconsin, Milwaukee, 53226, USA. xfzhang@mcw.edu
authors.forename: David X
authors.initials: DX
authors.lastname: Zhang
authors.forename: Lena
authors.initials: L
authors.lastname: Borbouse
authors.forename: Debebe
authors.initials: D
authors.lastname: Gebremedhin
authors.forename: Suelhem A
authors.initials: SA
authors.lastname: Mendoza
authors.forename: Natalya S
authors.initials: NS
authors.lastname: Zinkevich
authors.forename: Rongshan
authors.initials: R
authors.lastname: Li
authors.forename: David D
authors.initials: DD
authors.lastname: Gutterman
mesh_terms: D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000187:drug effects / Q000502:physiology*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005452:Fluoresceins / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
chemical_list: C513505:DT-2 compound; D004791:Enzyme Inhibitors; D005452:Fluoresceins; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010446:Peptide Fragments; D010455:Peptides; C064719:iberiotoxin; D006861:Hydrogen Peroxide; D017869:Cyclic GMP-Dependent Protein Kinases