Involvement Of Endothelin-1 Mechanism In Acute Ischemic Arrhythmia

Endothelin (ET) is a family of vasoconstrictive pcptides. El-i, the primary isoform of ET in the cardiovascular system, arises from preproendothelin-1 mRNA in various cells including endothelial cells, cardiomyocytes and smooth muscle cells. The actions of El-i are mediated by ETA and ET8 receptors, both present in myocardium and coronary arteries with ETA receptors being predominant. Myocardial hypoxia/ischemia is a strong stimulus for ET-l synthesis. Increased endogenous ET-l during ischemia tend to aggravate myocardlial ischemia via coronary constriction, and exert pro-ischemic and pro-arrhythmogenic effects as well. ETA and ET~vs receptor antagonists were reported to reduce infarct size and improve function of the ischemic heart, while the effects of such antagonists on ischemic arrhythinias have rarely been observed. Whether ET-l is arrhythmic or antiarrhythmic during myocardial ischemia remains controversial. To clarify the role of ET- i in the genesis of ischemic arrhytbmias, ETA receptor antagonist BQ61O and ET-l mRNA antisense oligodeoxynucleotides (AS-ODN) were administered to prevent the actions of endogenous El-i in cats and rats respectively, and the ischemic arrhythmias elicited by occlusion of the left anterior descending branch of coronary artery (LAD) were analyzed. To shed light on the mechanism of ET-l, the effects of BQ61O on hypoxia-induced changes in [Ca2']1 were observed in cultured neonatal rat cardiomyocytes. Hypoxia-induced injury and apoptosis in cultured cardiomyocytes were examined.1.Experimental model and methods(1)The acute myocardial ischemia was caused by the ligation of LAD in anesthetized cats, and BQ6IO was injected into LAD in l-2 mm. During a 60-mm period of LAD ligation, arterial blood pressure and ECG were recorded continuously. The ．7．Was were iwtfied bo ECG boe and estimand accowi tO incihaes,IUnnbers and score. StrUCtUre of the W aIter 30-min iSCMa was observedM oPtical ndcroscoPe and ebo ndcroscOpe'(2) Four PhOpeate AS-ODNs (ASl~AS4) comPleInentary to ET-l mRNA wereSynthswt and Phopeate sense onw (S4) and scramledoow(wtledAS4) were also Whed as cOntrOl. TwO hOurs befOre W occtheionin anesthetized rats, ASl~AS4, S4 or SCramledAS4 were boly injeCted toobserv changes in plasma ETl cOnCentratins, iSCMc peas andbo of the myocardium SUbected tO 30ch iSClera(3) CulW neOnatal rat cedOmyOcytes were coM tO hyPOkia by incubation in a3%O2-5%CO2 forSPfor at 37C. Cell aPOPtosis op TUNEL method andSUPematan LDH and SOD aCtw were mefor in noed, hyPoalc andBQ6l0ed hyPoalc cardiOInyOcytes. Besides, [Cah. was measured withca2+sensto nuorescen dye Fluo-3 Under a laser confocal ndcro8coPe. TheWa moaeI ed in [Cahi -- was nrofor by ~edOmyOctws with 95%Nz5%CO2 SatUrad DMEM solution addd with l rnMNas2O4.2. ReSults(l) EM of BQ6l0 on aCute iSChendc arrbythIulas and iSChndc mywtal rtin catsO In conbol cats rec~ nOnnal saline bel5), LAD ligation elicited severe ischedcwtas inchidin high incleres of VT and boble Ventricular fibrillation(l00% and 33.3%, resPeCtiVely), zunnero Vewhcular eCtOPic beats (VEBs; total:840 f l47), long tim VeDtricular Wnda (VT 68 l l8 sec), and a highWa score (AS, 4.56 l 0.39). In cats receiving BQ610 l.5, 3.0, 6.0 nmoljkg,the incleres of VT and VF the nUmbo of single VEBs, -- VEBs andVT and the Wa score were decreased dOsewt Ih 6.0 nmol/kgBQ6l0 pouP thell), no cats ds bo VT or VF and the total VEBs and ASSiedcantiy decreased to l5be38 and led rewtely@ M a POlndng ndcroscOpe, part of the iSCMc myOcardiUrn in cothel catsfailed to POlfor the light due tO denWn associand with ischeInim Howevr,such a PhenOInenon was nO observd in BQ6l0thed cats. NagarOlsen StahagshOwed red POM zons Mg Mon in the iSClerc myOcardiUm incontrol cats (tw, chIe the nd POsitiVe zons m relativey ndl in BQ6l0l.5 nmol/kg gnUP (~, and alinoSt no POsihve staiDin was observed in BQ6l06.0 nmoWg pe (f).@...