Objective: Gap junctions allow direct cell-cell communication and electrical coupling between individual myocytes. The component proteins of these junctions are the connexins (Cx). Adult working ventricular myocytes express Cx43 but normally lack detectable Cx40. Early in gestation, mice and humans express Cx40 in the developing trabeculated ventricle; this Cx40 disappears by birth. As studies on transgenic mice have demonstrated roles for connexins in cardiac morphogenesis, we investigated connexin expression in human congenital heart malformations.

Methods and Results: Connexin expression was studied in the right ventricles (RVs) of pre- and post-operative patients with tetralogy of Fallot (n=20; age 3 months to 27years), double chambered right ventricle (n=5; age 10 months to 14years) and controls without RV pathology (n=5; age 2 months to 11years). Immunoconfocal microscopy demonstrated localisation of gap junctions to the intercalated disk by age 2 years. In contrast to control hearts, Cx40 was prominently and heterogeneously expressed in the working right ventricular myocytes of all the diseased hearts. Electron microscopy demonstrated co-localisation of Cx40 and Cx43 within the same gap junction. Quantitative Western blot analysis showed that Cx40 expression represented up to 10% of total connexin in the RV.

Conclusion: There was significant expression of Cx40 in patients with RV outflow malformations; none in those without RV pathology. These findings were independent of whether the patients were pre- or post-operative, thus with markedly different underlying haemodynamics. Therefore our results suggest a lack of Cx40 repression during development which may be pivotal in the morphogenesis of these cardiac malformations.