Reduced connexin40 protein expression in the right atrial appendage of patients bearing the minor connexin40 allele (−44 G → A)

The occurrence of connexin40 (Cx40) minor polymorphism (44 G A) was increased in patients with idiopathic atrial fibrillation (AF), although its effect on atrial Cx40 protein expression is unknown. We aimed to evaluate whether alterations in Cx40 are directly linked to the development of AF, we studied the effect of this polymorphism on Cx40 expression and distribution in patients without any history of AF and in patients who developed post-operative AF. Hundred and eight patients (mean age 67 9 years), without a history of AF or conditions that predispose to AF, were included. During heart surgery, 10 cc blood was collected for DNA genotyping and the right atrial appendage was partly excised. Ten patients (9) were homozygous for the minor allele (AA, Group 1), 30 (28) were heterozygous (AG, Group 2), and 68 (63) were non-carriers (GG, Group 3). Ten age- and sex-matched tissue samples per group were analysed for Cx40 expression by: (i) real-time quantitative polymerase chain reaction (Q-PCR), (ii) western blotting, and (iii) immunohistochemistry on cryosections. Real-time quantitative polymerase chain reaction showed no significant differences of Cx40 mRNA among the groups. Western blot analysis, however, revealed a reduction in Cx40 protein in Groups 1 (36.4) and 2 (39.5) as compared with Group 3. Immunohistochemistry confirmed this reduction but indicated an unaltered subcellular distribution of the remaining Cx40. Incidence of post-operative AF (28) was age-dependent but unrelated to the presence of the polymorphism or fibrosis. Presence of the Cx40 minor allele (44 G A) results in a uniform down-regulation of right atrial appendage Cx40 protein which was not significantly related to development of post-operative AF