Heterogeneous Expression of Gap Junction Channels in the Heart Leads to Conduction Defects and Ventricular Dysfunction

Abstract

Background-Heterogeneous remodeling of gap junctions is observed in many forms of heart disease. The consequent loss of synchronous ventricular activation has been hypothesized to result in diminished cardiac performance. To directly test this hypothesis, we designed a murine model of heterogeneous gap junction channel expression. Methods and Results-We generated chimeric mice formed from connexin43 (Cx43)-deficient embryonic stem cells and wild-type or genetically marked ROSA26 recipient blastocysts. Chimeric mice developed normally, without histological evidence of myocardial fibrosis or hypertrophy. Heterogeneous Cx43 expression resulted in conduction defects, however, as well as markedly depressed contractile function. Key Words: ion channels Ⅲ contractility Ⅲ conduction Ⅲ genes Ⅲ arrhythmia G ap junctions play a pivotal role in the coordinated excitation of the heart. 1 Formed from the assembly of a family of proteins known as connexins, gap junction channels in the myocardium are preferentially targeted to the intercalated disks between adjacent myocytes and account in part for anisotropic conduction in normal cardiac tissue. 2 In a wide spectrum of cardiac disease states, abnormalities in connexin subcellular localization is observed. [3][4][5][6][7][8][9][10] Increasing experimental evidence, including recent murine genetic studies, links this pathological remodeling of gap junctions to cardiac conduction abnormalities and rhythm disturbances. 8,11,12 Remodeling of gap junctions is often focal, a spatial pattern that might result in discrete areas of conduction defects within the myocardium. 7,13 Although experimental data are lacking, it has been hypothesized that remodeling could disrupt wave-front propagation, interfere with coordination of myocyte contraction, and diminish contractile performance. 7,14 Accordingly, in this study, we designed a model of heterogeneous gap junction expression in the heart to test the hypothesis that loss of synchronous ventricular activation diminishes cardiac contractile performance. We generated chimeric mice, formed from connexin 43 (Cx43)-deficient embryonic stem (ES) cells and wild-type or genetically marked ROSA26 recipient blastocysts, to model the heterogeneous pattern of gap junction expression typical of diseased myocardium. In contrast to the uniform conduction slowing in Cx43 conditional knockout mice, 12 optical maps of chimeric hearts with voltage-sensitive dye showed highly irregular epicardial activation profiles. Moreover, chimeric mice developed significant contractile defects, supporting the hypothesis that loss of synchronous electrical activation of the ventricular myocardium from gap junction remodeling leads to systolic dysfunction. Methods Gene Targeting and Production of Cx43؊/؊ Chimeric MiceThe generation of Cx43 ϩ/flox ES cells (129/Sv) harboring a "floxed" Cx43 allele has been described previously. Western Blot AnalysisWestern blot analyses were performed with a rabbit polyclonal antibody to Cx43 and a mouse monoclonal antibody to tubulin (...

Cortactin Is Required for N-cadherin Regulation of Kv1.5 Channel Function

“…Several other mutant mouse models are able to support sustained ventricular arrhythmias (10), but these require provocative stimuli, such as exercise with administration of adrenergic agents. To date, only the heart-specific connexin43 (Cx43) (11), vinculin (12), and N-cadherin (7) knock-out mice have been shown to die prematurely from spontaneous sustained ventricular tachyarrhythmias. Because of the arrhythmic propensity of the N-cad CKO mice and the ease of inducible sustained arrhythmias, it has served as a model for the study of basic mechanisms of arrhythmia.…”

Downregulated myocardial connexin 43 and suppressed contractility in rabbits subjected to a cholesterol-enriched diet

“…5,6 Alterations in the organization of cardiac gap junctions and expression of Cx43 can cause predisposition to arrhythmia, uncoordinated contraction, and overall diminished myocardial function in various pathologic conditions. [5][6][7][8][9] Using chimeric mice created from Cx43-deficient stem cells and blastocysts, Gutstein et al 10 have demonstrated that spatially heterogeneous Cx43 downregulation is indeed linked to disturbances in electromechanical function in terms of both irregular epicardial conduction patterns and contractile dysfunction. 10 Dietary hypercholesterolemia has been also shown to induce contractile dysfunction independent of vascular disease, characterized by a decrease in the maximum rate of shortening and relaxation in a papillary muscle preparation, 11 although this finding has not been confirmed in isolated intact hearts.…”

“…[5][6][7][8][9] Using chimeric mice created from Cx43-deficient stem cells and blastocysts, Gutstein et al 10 have demonstrated that spatially heterogeneous Cx43 downregulation is indeed linked to disturbances in electromechanical function in terms of both irregular epicardial conduction patterns and contractile dysfunction. 10 Dietary hypercholesterolemia has been also shown to induce contractile dysfunction independent of vascular disease, characterized by a decrease in the maximum rate of shortening and relaxation in a papillary muscle preparation, 11 although this finding has not been confirmed in isolated intact hearts. 12 Ultrasonic tissue characterization (UTC) with cardiac cycle-dependent variation of integrated backscatters (CVI) has been shown to be representation of intrinsic myocardial contractility and a potential indicator of early systolic dysfunction.…”

The Remodeling of Connexins Localized at Pulmonary Vein – Left Atria in Triggering and Maintenance of Atrial Fibrillation

“…Previous studies have demonstrated that loss of cell-cell coupling is highly arrhythmic (Chaldoupi et al, 2009), however, a detailed understanding of arrhythmia dynamics has been lacking. With respect to mechanistically link a primary perturbation of gap junction function with arrhythmia, conduction properties, arrhythmia dynamics, and cellular electrophysiological characteristics have been detected (Zhou et al, 2008;Severs et al, 2008;Gutstein et al, 2001). Accumulative evidences showed that ventricular gap junctions contain at least 20 times more connexin43 than connexin40, while atrial gap junctions contain much more connexin40 than connexin43 (Kontogeorgis et al, 2008;Lin et al, 2010).…”