Connexin 40 polymorphism and protein expression in the right atrial appendix in patients without atrial fibrillation.

Connexin 40 (Cx40) protein is one of the most important connexins expressed in
the atria which form the gap junctions. Gap junctions are clusters of
transmembrane channels that link adjoining cells and mediate cell-to-cell
electrical coupling and communication. The role thus of Cx40 on the propagation
of the electrical stimulus in the heart is essential. Alterations in the
organization of gap junctions and connexins expression are well established as
a consistent feature of human heart disease and may lead to arrhythmias. On the
other hand, studies in animals have also shown that heart arrhythmias, like
atrial fibrillation (AF) can lead to changes in the distribution, intercellular
orientation and expression of the connexin proteins. In patients with chronic
AF quantitative and qualitative alterations in Cx40 expression of the right
atrial appendix (RAA) have been shown and these changes could result in changes
of the electrophysiologic properties of the atrial tissue, thereby increasing
vulnerability to AF. Research from our department has shown that patients with
idiopathic AF have a higher prevalence of Cx40 polymorphism (-44AA coupled with
+71 allele). Cx40 polymorphism occurs in 7% of the general population. The
direct relation however between Cx40 gene polymorphism and Cx40 protein
expression in the atria has not yet been investigated.

The main objective of this study is to investigate the relation between Cx40
polymorphism and protein expression in the general population and patients
without a history of AF.

This study was designed as a monocenter observational cross-sectional study.
The participating center is the UMC Utrecht. Patients scheduled for cardiac
surgery and free of AF will be asked to participate in this study. After
informed consent patients will be included. During cardiac surgery the right
atrium is incised at the base of the right atrial appendix (RAA) for the
canulation of the heart- lung machine. The collection of a small part (0.5x0.5
cm) of the RAA does not do extra harm to the patient. This part of the RAA will
be immediately snap frozen in liquid nitrogen and stored at -80 degrees and
taken to the department of medical physiology for further analysis. Also, 5ml
of blood will be obtained for genomic DNA extraction. First, the DNA samples
will be genotyped for the Cx40 polymorphism at nucleotide position -44 (G*A),
which is located within the regulatory region of the Cx40 gene. Sequencing will
be performed on purified Polymerase Chain Reaction products and the samples
will be run and analyzed on an ABI automated sequencer. Seven percent of the
patients will be homozygote (group 1) for the polymorphisms. According to the
Hardy-Weinberg equilibrium, 39% of the patients will be heterozygote (group 2)
and the others will not carry the minor allele (group 3). An equal number of
cardiac tissue samples from all these three groups will be used for further
tissue analysis (Western-Blotting, reverse transcript PCR, immunohistology). We
will look for differences in Cx40 protein expression among these three groups.

Participation in this study will have no additional risk to the patient. The
excision of a small part of the right atrial appendix during surgery does not
do extra harm to the patients. Approximately 5ml of extra blood will be drawn
during a vena puncture which is a standard procedure for this type of
operation.