Abstract 4406: Identification and Biophysical Properties of Novel Connexin40 Mutations Associated with Idiopathic Atrial Fibrillation
Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. In lone AF, the majority of cases are non-familial and a genetic basis for the arrhythmia is not routinely considered. We have recently demonstrated that mutations of the connexin40 (Cx40) gene may be detected in atrial tissue only, and absent from lymphocyte DNA analysis of the same patient, defining some cases of lone AF to be a somatic genetic disease. We now describe the identification and biophysical properties of 2 novel Cx40 mutations found in a cohort of patients with lone AF.
Methods: A cohort of 75 lone AF patients underwent genetic screening of lymphocyte DNA for genetic variants of the Cx40 gene (GJA5) using heteroduplex analysis. Abnormal conformers were directly sequenced. Two novel Cx40 mutations were identified from 2 patients, Phe30Leu and Gly311Ser, respectively. Protein trafficking studies were performed in Hela cells. Electrophysiologic studies were undertaken in N2A cells and Xenopus oocytes injected with wild type or mutant Cx40.
Results: Protein trafficking studies in Hela cells demonstrated appropriate localization and plaque formation of mutant Cx40 proteins to sites of cell-to-cell contact. Electrical cell-to-cell coupling of the Gly311Ser-Cx40 mutant was significantly reduced as compared to wt-Cx40. Electrical coupling of the Phe30Leu-Cx40 mutant demonstrated similar junctional conductance to wt-Cx40. However, in single Xenopus oocytes, Phe30Leu-Cx40 hemichannel currents were significantly greater than oocytes injected with similar amounts of wt-Cx40.
Conclusion: These results confirm our previous findings that a loss of gap junction cell-to-cell coupling may predispose the atria to fibrillation. In addition, we describe the finding of enhanced connexin hemichannel function as a potential novel mechanism promoting vulnerability to atrial fibrillation.