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Updated: Aug 9, 2026
High-resolution Optical Mapping of the Mouse Sino-atrial Node
Published on: December 2, 2016
Sodium channel distribution within the rabbit atrioventricular node as analysed by confocal microscopy
K Petrecca1, F Amellal, D W Laird
1Department of Physiology, McGill University, Montreal, Quebec, Canada.
Insights
This study investigated sodium channel and connexin43 distribution in rabbit atrioventricular (AV) nodes. Reduced expression in the AV node
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Electrophysiology
Background:
- Sodium channels are crucial for cardiac impulse conduction.
- Connexin43 forms gap junctions, essential for cell-to-cell communication in the heart.
- The specific distribution of these proteins in the atrioventricular node is not fully understood.
Purpose of the Study:
- To investigate the spatial distribution of sodium channels and connexin43 within the rabbit atrioventricular node.
- To correlate protein expression patterns with functional properties of AV nodal conduction.
Main Methods:
- Immunohistochemistry and confocal microscopy were used on rabbit AV nodal tissue.
- Antibodies against sodium channels (interdomain 3-4 region) and connexin43 (carboxyl terminus) were employed.
- Immunofluorescence was quantified and localized within different AV nodal cell populations.
Main Results:
- Sodium channels and connexin43 were abundant in atrial and ventricular myocardium, localized to membranes and T-tubules (sodium channels) and intercalated discs (connexin43).
- In the AV node, peripheral transitional cells showed high expression, similar to myocardium.
- Central midnodal cells exhibited significantly reduced or absent sodium channel and connexin43 immunofluorescence.
Conclusions:
- A gradient of sodium channel and connexin43 expression exists within the rabbit AV node.
- The paucity of these proteins in the central AV node suggests a mechanism for slowed impulse conduction.
- This differential expression pattern is critical for the unique electrophysiological properties of the AV node.
Abstract:
1. Paired 20 microns thick sections of fresh frozen tissue taken from the frontal plane of the rabbit atrioventricular (AV) nodal region were processed for histology and immunohistochemistry. Confocal microscopy was used to image the distribution of sodium channels using IgG (R12) developed against a highly conserved sequence in the interdomain 3-4 region of cloned sodium channels. 2. In ventricular and atrial cells, sodium channel immunofluorescence was localized to lateral membranes and T-tubules. In the open AV node, levels of sodium channel immunofluorescence in the transitional cell zone and in the lower nodal cell tract were comparable to that found in the atrial and ventricular myocardium. 3. In the enclosed AV node a gradation of sodium channel immunofluorescence is present such that peripherally located circumferential transitional cells display high levels of immunofluorescence, comparable to that of atrial and ventricular myocardium, while centrally located midnodal cells display decreased levels of or no immunofluorescence. 4. In order to correlate the distribution of sodium channels with the distribution of gap junctions, we used IgG directed against the carboxyl terminus of connexin43 (CT-360). Ventricular cell immunofluorescence was localized primarily to the intercalated disk region, while in the AV node, the pattern of distribution was found to be similar to that of sodium channels. 5. The reduced levels of and/or absence of immunofluorescence in the midnodal cell region indicates a paucity of sodium channel and connexin43 protein expression in this region of the AV node that would favour slow impulse conduction.
