Cell Coupling Between Ventricular Myocyte Pairs From Connexin43-Deficient Murine Hearts

Abstract

Abstract-Mice with cardiac-restricted inactivation of the connexin43 gene (CKO mice) have moderate slowing of ventricular conduction and lethal arrhythmias. Mechanisms through which propagation is maintained in the absence of Cx43 are unknown. We evaluated gap junctional conductance in CKO ventricular pairs using dual patch clamp methods. Junctional coupling was reduced to 4Ϯ2 nS (side-to-side) and 11Ϯ2 nS (end-to-end), including 21% of cell-pairs with no detectable coupling, compared with 588Ϯ104 nS (side-to-side) and 558Ϯ92 nS (end-to-end) in control cell-pairs. Key Words: gap junctions Ⅲ connexin Ⅲ remodeling Ⅲ arrhythmias C hanges in gap junction structure and function 1 in pathological conditions (gap junction remodeling) may contribute to arrhythmogenesis. 2-9 Gap junction protein quantity is reduced in heart failure, cardiomyopathy, and ischemia 2,3,5 and is redistributed around the cell perimeter in infarct border zones. 3,4 Junctional conductance is decreased in ischemia and ventricular hypertrophy. 6 -9 These changes are associated with propagation slowing and sometimes arrhythmias, although other pathological changes in diseased myocardium are also likely to play a role. Recently, genetic strategies have been used to specifically examine relationships between cardiac gap junction expression and function. 10 -14 Using a conditional gene-targeting strategy, we generated mice deficient in myocardial Cx43 (CKO mice) and demonstrated that such mice succumb to lethal ventricular tachyarrhythmias. 10 Interestingly, despite the virtual loss of the principal connexin responsible for ventricular cell coupling, effects on conduction velocity were relatively modest, with about 50% slowing. 10 In this study, we directly measured transjunctional conductance in ventricular myocyte pairs from CKO mice. We found that conductance is markedly reduced to 1% to 2% of controls. This level of conductance is predicted by theoretical studies to have a much greater conduction slowing effect [15][16][17] than observed in vivo in this model, 10 suggesting that additional mechanisms support impulse propagation when gap junctional conductance is severely reduced. 18 Materials and Methods Murine ModelGap junctional conductance was investigated in ventricular myocyte cell pairs obtained from a gene-targeted murine model in which the Cx43 gene was conditionally inactivated exclusively in cardiomyocytes by use of the Cre/loxP system (CKO mice). 10 Immunohistochemical studies and Western blot analysis have demonstrated that as many as 95% of myocytes from these CKO mice fail to express Cx43. 10 For controls, we used littermates that are homozygous "floxed" but do not express Cre recombinase and express wild-type levels of Cx43. 19 We also studied a heterozygous group that has a Ϸ50% reduction in Cx43 in the heart (unpublished data, 2003). Preparation of Ventricular MyocytesAnimals were cared for according to the guiding principles in DHEW (NIH) No. 85-23. Protocols were approved by IACUC at New York University and Columbia. CKO and con...

Evolutionarily conserved intercalated disc protein Tmem65 regulates cardiac conduction and connexin 43 function

“…Germline deletion of the Cx43 gene in mice leads to perinatal lethality due to developmental cardiac malformation 30 . In contrast, mice with cardiac-restricted inactivation of Cx43 are viable; however, they develop ventricular tachyarrhythmias leading to sudden cardiac death within 2 months 50,51 . Several mutations in Cx43 have previously demonstrated serious conduction abnormalities both in mouse models and in human patients 47,[52][53][54][55] .…”

Alteration of Cholinergic Anti‐Inflammatory Pathway in Rat With Ischemic Cardiomyopathy–Modified Electrophysiological Function of Heart

“…In addition, Cx43, which contributes to intercellular communication and electrical coupling, is the principal component of ventricular gap‐junction proteins. Genetically engineered Cx43‐deficient (Cx43 +/− or Cx43 −/− ) mice have been reported to be markedly susceptible to ischemia‐induced ventricular tachycardia 36, 37, 38. Ando et al39 reported that increased vagal tone could prevent the loss of Cx43 during acute MI and thus exert antiarrhythmogenic effects.…”

Genomics, heart failure and sudden cardiac death

“…Importantly, animal studies provide compelling evidence that reduced expression of connexin 43 accelerates the onset and increases the incidence, frequency, and duration of ventricular tachyarrhythmias [45]. Mice deficient in connexin 43 not only experienced more spontaneous ventricular arrhythmias, but also VT could be more easily induced when compared to wild-type control mice [46,47]. Despite this compelling evidence of the critical role of connexins in arrhythmogenesis, contemporary research in this field has so far focused on evaluating altered expression of connexin mRNA in patients with HF and there have been no systematic studies performed to identify common connexin genetic variants in cohort populations at high-risk for SCD.…”