Cx 40 And Cx 43 Variation In Atria Of Patients Suffering Coronary Heart Disease With Or Without Atrial Fibrillation

Background:The mechanism of onset and maintenance of AF is not fully understood,though many recent studies have allowed an improvement in the comprehension of the pathophysiology of the arrhythmia,for onset of AF,Some researches on mechanism of onset dicovered the focal discharge could resulted in paroxysm AF in the vena cava system such as the vena coronaria,the superior and inferior vena cava and pulmonary vena.Some basic researches also found the fact that the vena cava system of the heart existed in the myocardial sleevers which shared the commonness with the conducting system such as the sino-atrial node,atrial ventricular node and his bundle.Meanwhile some dataes found the similarity in the ultramicro structure between the myocardial sleeves and the node-like cells in the sinoatrial node, suggesting the potential pacing founction of the node-like cells in the pulmonary vane.Therefore,The difference of embryo origin between myocardial sleeves and atrium tissue bring about the difference in electrophysiological characteristics,which is important in AF onset. Besides,An increase in sympathetic tone,cardiac fat pad and vascular nerves in chambers heart is considered by many researchers as an important factor in initiating and maintaining AF,which first result in atrial premature beats,paroxysmal atrial tachycardia by diminish autorhythmic cell membrance potential,after-depolarization and triggers.For maintenance of AF,many recent studies have allowed that atrial remodeling is the important reentry substrate of AF,which include atrial electroical remodeling and atrial anatomical remodeling.Atrial electroical remodeling means shorten of atrial efective refractory period and action potential period and slow conduction velocity,while Atrial anatomical remodeling means the changes of atrium tissue,cells and ultramicrostructure,meanwhile the contractile remodeling.The changes including the concentration of the ions,the activity and the protein phosphorylation of the ion channel appeared in several seconds or minutes after the AF,followed by the subsequent mRNA and protein expression in the next hours and days,among which there was the connexin.The hypertrophy and apoptosis of the atrial myocardial cells, the inflammatory cell infiltraton and the interstitial fibrosis occurred after these changes.Atrial electroical remodeling and the spatial distribution heterogeneity of the structure remoding,the extention of the myocardial sleeves in vena cava system and the atrial cells,and the gap junction among the myocardial sleeves comprise of the maintenance mechaniasm. The electrophysiological mechanisms of AF are principally based on traditional single cell membrane channels,and less concern on current conduction between cells.Moreover,therapy and prophylaxis of recurrences are not always successful.It is possible that this is due to an'empirical'use of drugs in the prevention of recurrences,i.e.not based on precise knowledge of triggering mechanisms and arrhythmia substrates.In fact,all of myocardium is involved in any type of arrhythmia(including AF);arrhythmia is no fewer determined by passive current conduction than membrane channels.Accounting for AF is incomplete regardless of passive conduction between cells.Any contribution to a better understanding of trigger mechanisms,substrate modifications and the role of the autonomic nervous system may be helpful in achieving the prevention of AF.It has been proved that gap junction is the only structure responsible for intercellular curent conduction.Gap junction is a specialized regions of the membranes of adjacent cells,containing arrays of densely packed intercellular channels that directly connect the cytoplasmic compartments of neighboring cells and permit intercellular passage of ions and small molecules.Gap junctions maintain cellular homeostasis by allowing communication between adjacent cells.In the heart,gap junctions provide the pathways for intercellular current flow,enabling coordinated action potential propagation.Gap-junctional channels are constructed from connexins (Cxs),a multigene family of conserved proteins termed connexins.In the mammalian heart,Single gap junction channel is composed of six connexin that abbreviate Cx by the molecular weight of the specific protein.It has been established that mammalian cardiac express Cx31.9, Cx37,Cx40,Cx43 and Cx45.but different tissue of the heart express different amounts and combinations of these connexins,Cx43 was confirmed to be abundantly in all four chambers in human heart,Cx45 expression appears to be within the atrioventricular conduction system and Cx40 is present specifically in the atrium and in the specialized conducting system.Gap junctions span the plasma membrane of two adjacent cells,with each cell contributing half the channel,a hemichannel, or connexon.A connexon from one cell docks in the extracellular space with a connexin from an opposing cell to form a complete gap-junction channel,allowing adjacent cells to be coupled,termination links are more than latero-links.Changes of Cx40 in quantity,phosphorylation and spatial distribution result in changes of GJ in construction,areas,density, characteristic and spatial distribution,then conduction velocity and conduction anisotropy in atrium myocytes changes,microreentry occurs, which facility AF.Cx40 gap junction channel was speculated to play critical roles in atria arrhythmia and AF.Although there are a few of researchs about Cx40 and Cx43 on mechanisms of rheumatic heart disease AF,Our study aim to reveal the changes of Cx40 and Cx43 expression,spatial distribution patern,and their morphology in human atrial myocardium from coronary heart disease.Whole experiment is composed of three parts as below: Part one Changes of connexin40 in dilated left atria of patients suffering coronary heart disease with or without atrial fibrillationObjective:To explore the effects of connexin 40 and the left atrium size in the AF by studying the expression of Connexin40 in Atrium of patients suffering from coronary heart disease with or without AD or AF.Methods:26 patients with Coronary heart disease undergoing cardiac surgery for coronary artery bypass graft were involved in this study and were divided into three groups according to the left atrial size and rhythm.All patients were examined by coronary arteriongraphy,echocardiogram and ECG before surgical operation.6 cases with AF and left atrial dilatation (AF+AD),8 with sinus rhythm and left atrial dilation(SR+AD)and 12 sinus rhythm without atrial dilation(SR)Expression of Cx40 was detected by immunoblotting assay(western blot).Results:1.No obvious change was observed in the Cx40 expression in right atrium in the three groups(P＞0.05).2.No obvious change was observed in the Cx40 expression in AF+AD group and SR+AD group(P＞0.05).3.Comparing with the Cx40 expression in right atrium of the SR group,AF+AD group and SR+AD group,there was significantly decreased than that in the left atrium in AF+AD group and SR+AD group(P＜0.01).Conclusion:The decrease expression of Cx40 is relation with left atrial dilatation, the decrease expression of Cx40 and left atrial dilatation could be an important agents in the occurrence and maintenance of AF. Part two Changes of connexin43 in dilated left atria of patients suffering coronary heart disease with or without atrial fibrillationObjective:To explore the effects of connexin 43mRNA and connexin 43 and the left atrium size in the AF by studying the expression of Connexin43 mRNA and connexin 43 in Atrium of patients suffering from coronary heart disease with or without AF.Methods:26 patients with Coronary heart disease undergoing cardiac surgery for coronary artery bypass graft were involved in this study and were divided into three groups according to the left atrial size and rhythm.All patients were examined by coronary arteriongraphy,echocardiogram and ECG before surgical operation.6 cases with AF and left atrial dilatation (AF+AD),8 with sinus rhythm and left atrial dilation(SR+AD)and 12 sinus rhythm without atrial dilation(SR).Expression of Cx43mRNA was detected by RT-PCR.Expression of Cx43 was detected by immunoblotting assay(western blot).Results:No obvious change was observed in the Cx43mRNA and Cx43 expression in left and right atrial myocytes in the three groups(P＞0. 05).Conclusion:The expression of Cx43mRNA and Cx43 is not relation with left atrial dilatation and the expression of Cx43mRNA and Cx43 contribute less than the expression of Cx40 in the occurrence and maintenance of AF. Part three Disorganization of connexin40 distribution in dilated left atria of patients suffering coronary heart disease with or without atrial fibrillationObjective:For immunodetection of gap junctions,primary antibody-bound Cx40 and cadherin were visualized using fluorescent isothiocyanate -conjugated anti-mouse immunoglobulin(Ig)G and Texas Red conjugated anti-rabbit IgG.The labelled samples were examined using a confocal microscope and light microscope to explore the effects of connexin 40 in the AF patients with Coronary heart disease.Methods:26 patients with Coronary heart disease undergoing cardiac surgery for coronary artery bypass graft were involved in this study and were divided into three groups according to the left atrial size and rhythm. All patients were examined by coronary arteriongraphy,echocardiogram and ECG before surgical operation.6 cases with AF and left atrial dilatation(AF+AD),8 with sinus rhythm and left atrial dilation(SR+AD) and 12 sinus rhythm without atrial dilation(SR).The spatial distribution pattern of Cx40 were detected through light microscope and confocal lasers canning microscopy assay.Results: 1.No obvious change was measured in the size and density of Cx40 gap junction in right atrium in all the 3 groups(P＞0.05).2.Comparing with the control group,the size of Cx40 disk area in termination links and in lateral abutment in left atrium was markedly larger in AF+AD group and SR+AD group than those of the controls(P＜0.01).3.The size and density of Cx40 gap junction in left atrium in the AF+AD group and SR+AD group showed on difference.4.The results revealed a striking loss of central small Cx40-gap junctions at the intercalated disk of AF patients.The reduction of Cx40 gap junctions within the intercalated disk was remarkable in the LA and occurred concomitantly with an enlargement of disk area.Conclusion:Changes of the size increase and density decrease of Cx40 gap junction could be an important agent in the occurrence and maintenance of AF.