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Published on: February 26, 2017
Immunoelectron microscopic visualization of the gap junction protein connexin 40 in the mammalian heart
A De Mazière1, L Analbers, H J Jongsma
1Department of Physiology, University of Amsterdam, The Netherlands.
Insights
Connexin 40 (cx40) gap junctions are found in specific mammalian heart regions, differing from connexin 43 (cx43). This distribution may influence cardiac electrical conduction speed.
Area of Science:
- Cardiovascular Biology
- Cellular Electrophysiology
- Molecular Cardiology
Background:
- Mammalian cardiac myocytes are electrically coupled via gap junctions, essential for coordinated heartbeats.
- Cardiac gap junctions are primarily composed of connexin 43 (cx43), but connexin 40 (cx40) and connexin 45 (cx45) are also present.
- Understanding the distribution of different connexin proteins is crucial for comprehending cardiac electrical properties.
Purpose of the Study:
- To investigate the ultrastructural distribution of connexin 40 (cx40) in various mammalian cardiac tissues.
- To compare the localization of cx40 with the predominant connexin 43 (cx43) in atrial and ventricular myocardium.
- To explore the potential functional implications of cx40 distribution on cardiac electrical conduction.
Main Methods:
- Utilized immunogold labeling with a specific antibody to trace the ultrastructural distribution of cx40.
- Examined cardiac tissues from rabbit and rat, including atria, ventricles, and false tendons.
- Performed double labeling experiments to simultaneously visualize cx40 and cx43 distribution.
Main Results:
- Connexin 40 (cx40) was identified in gap junctions of rabbit right atrium and left ventricle false tendons.
- Cx40 labeling in rabbit ventricular walls required higher antibody concentrations, suggesting lower abundance.
- In rat myocardium, cx40 was found in limited patches within gap junctions predominantly composed of cx43, particularly in the atrium.
Conclusions:
- Connexin 40 (cx40) exhibits a distinct topographical distribution within mammalian cardiac tissues compared to connexin 43 (cx43).
- The differential distribution of cx40 and cx43, with cx40 having higher conductance, may contribute to regional variations in cardiac impulse conduction velocity.
- Further research into connexin heterogeneity is warranted for a comprehensive understanding of cardiac electrophysiology.
Abstract:
In mammalian myocardium, myocytes are electrically coupled by gap junctions, which are collections of membrane channels spanning the intercellular gap. Each channel is composed of twelve protein molecules--six in each membrane--enclosing a pore of 2 nm diameter. In addition to the main cardiac gap junction protein connexin 43 (cx43), two other constituents, connexin 40 (cx40) and connexin 45 (cx45), recently have been identified. In this study, the ultrastructural distribution of cx40 has been traced in several mammalian cardiac tissues, using a specific antibody and immunogold labeling. In rabbit, cx40 was found in gap junctions between myocytes of the right atrium as well as in the false tendons of the left ventricle. Labeling within the free ventricular wall could be obtained only with higher primary antibody concentrations. In rat atrial and ventricular working myocardium a similar distribution of label was observed. Double labeling of cx40 and cx43 in rat atrium, with 5 nm and 15 nm gold particles respectively, demonstrates limited patches of cx40 in gap junctions otherwise homogeneously labeled for cx43. Since cx40 has a much higher single channel conductance than cx43, topographical differences in their relative distribution might contribute to regional differences in conduction velocity of the cardiac impulse.
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