MitoKATP channel activation suppresses gap junction permeability in the ischemic myocardium by an ERK-dependent mechanism

Abstract

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. 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. 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.