The functional significance of human connexin40 mutations on atrial physiology and propensity to atrial arrhythmia

Abstract

Objective: To characterise the phenotype of the human connexin40 mutations P88S, G38A, and A96S in rat hearts and primary cardiomyocyte cultures. Background: Patch clamping of transfected non-cardiomyocytes revealed that P88S, G38A, and A96S, identified in patients with atrial fibrillation (AF), impair gap junction conductance. Methods: Left atria of adult Sprague-Dawley rats were transduced in vivo (lentivirus) with wtCx40, P88S, G38A, A96S, or eGFP (n=6 per group). Electrophysiology studies (EPS) were performed prior to and 7 days after transduction. Atria were assessed for connexin expression, mRNA levels, inflammation and fibrosis. Primary cardiomyocyte cultures were also transduced (n=6 per transgene); conduction velocities (CV) and protein expression were assessed at 96hrs. Results: Day7 P wave and induced AF durations were longer in mutant groups compared to wtCx40 controls (p<0.05). Inflammation, fibrosis and heart/body weight ratios were similar. A96S culture CV’s were slower compared to wtCx40. P88S and wtCx40 CV’s were similar but slower compared to eGFP (p<0.01). G38A cultures fibrillated spontaneously and were non-capturable. Immunofluorescence revealed that P88S and G38A reduced native connexin43 myocyte coupling. A96S and wtCx40 appeared to co-localise with membranous conneixn43. Connexin43 mRNA levels were similar between groups. Conclusion: A96S, G38A, and P88S slow conduction and increase propensity for AF.