MitoKATP channel activation suppresses gap junction permeability in the ischemic myocardium by an ERK-dependent mechanism.
BACKGROUND
Ischemic preconditioning accelerates suppression of gap junction (GJ) permeability during myocardial ischemia, and GJ blockers reduce infarct size. We hypothesized that the mitochondrial ATP-sensitive K+ (mitoKATP) channel is one of the mechanisms regulating GJ permeability through the mitogen-activated protein kinase ERK, leading to cardioprotection.


RESULTS
In isolated rabbit hearts, tissues were sampled before and after infusion of diazoxide, a selective mitoKATP channel opener, and their intercalated disc-rich fractions were obtained for immunoblotting of mitogen-activated protein kinases. GJ permeability in the myocardium was assessed by using Lucifer yellow as a tracer of GJ communication. Infarction was induced by 30-min global ischemia/2 h reperfusion, and infarct size was expressed as a percent of area-at-risk (%IS/AR). Diazoxide (100 microM) induced phosphorylation of ERK1/2 and 279Ser/282Ser of connexin-43, a GJ subunit protein, and phospho-ERK1/2 was co-immunoprecipitated with connexin-43 in the diazoxide-treated myocardium. This ERK1/2 phosphorylation by diazoxide was inhibited by N-2-mercaptopropionyl-glycine, a free radical scavenger. Diazoxide at 10 and 100 microM reduced intercellular transport of Lucifer yellow during ischemia by 44% and 69%, respectively, and this effect of diazoxide on GJ communication was abolished by PD98059, an ERK inhibitor. Pretreatment with 10 microM and 100 microM diazoxide reduced %IS/AR from 57.1+/-3.7% to 21.5+/-10.5% and 5.0+/-1.3%, respectively. PD98059 abolished cardioprotection by 10 microM diazoxide but not that by 100 microM diazoxide.


CONCLUSIONS
Opening of the mitoKATP channel activates ERK1/2 via free radicals and induces ERK-mediated suppression of GJ permeability. This suppression of GJ permeability may partly contribute to cardioprotection afforded by mitoKATP channel activation.
Naitoh
Kazuyuki
K
Second Department of Internal Medicine, Sapporo Medical University School of Medicine, South-1 West-16, Chuo-ku, Sapporo 060-8543, Japan.
Ichikawa
Yoshihiko
Y
Miura
Tetsuji
T
Nakamura
Yuichi
Y
Miki
Takayuki
T
Ikeda
Yoshihiro
Y
Kobayashi
Hironori
H
Nishihara
Masahiro
M
Ohori
Katsuhiko
K
Shimamoto
Kazuaki
K
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D018031:Connexin 43 / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D017629:Gap Junctions / Q000378:metabolism*; D015151:Immunoblotting; D047468:Immunoprecipitation; D020935:MAP Kinase Signaling System; D008929:Mitochondria, Heart / Q000201:enzymology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017202:Myocardial Ischemia / Q000378:metabolism* / Q000473:pathology; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D011817:Rabbits; D008625:Tiopronin / Q000494:pharmacology
D018031:Connexin 43; D004791:Enzyme Inhibitors; D005419:Flavonoids; D016166:Free Radical Scavengers; D000255:Adenosine Triphosphate; D008625:Tiopronin; D020929:Mitogen-Activated Protein Kinase Kinases; D003981:Diazoxide; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one