The atrioventricular node and bundle in the ferret heart: a light and quantitative electron microscopic study

Area of Science:

• Cardiovascular Anatomy
• Cardiac Electrophysiology
• Cell Biology

Background:

• The atrioventricular (AV) junction is critical for cardiac impulse conduction.
• Understanding its cellular organization is key to comprehending heart rhythm.

Purpose of the Study:

• To elucidate the structural organization and ultrastructural characteristics of ferret heart AV junctional cells.
• To identify distinguishing features between atrial muscle cells and AV junctional conduction tissues.

Main Methods:

• Light microscopy and wax-model reconstruction for gross organization.
• Quantitative electron microscopy for ultrastructural analysis.
• Stereological analysis of cellular components and membrane specializations.

Main Results:

• The AV junction exhibits distinct subdivisions: transitional zone, AV node (coronary sinus, superficial, deep portions), and AV bundle (multiple segments).
• AV junctional conduction cells possess fewer myofibrils and lack T-tubules compared to atrial muscle cells.
• Differences in mitochondrial and myofibril content, and surface membrane specializations (desmosomes, fasciae adherentes, gap junctions) distinguish cell types and regions.

Conclusions:

• Cellular morphology and membrane specializations provide reliable criteria for differentiating atrial muscle cells from AV junctional conduction tissues.
• Specific surface membrane characteristics effectively distinguish between different regions within the AV junctional conduction system.