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To excite a heart: a bird's view
J R Sommer1, E Bossen, H Dalen
1Department of Pathology, Duke University Medical Center, Durham, N.C.
Acta Physiologica Scandinavica. Supplementum
|January 1, 1991
Summary
Ultrastructural studies of avian cardiac muscle reveal specialized conduction fibers in ratite hearts. These findings explain how excitation triggers contraction, adapting to different heart sizes and rates.
Area of Science:
- Cardiovascular Biology
- Comparative Anatomy
- Cellular Electrophysiology
Background:
- Avian cardiac muscle exhibits unique structural adaptations for excitation-contraction coupling.
- Previous studies suggest a link between conduction system geometry and cardiac function in birds.
Purpose of the Study:
- To investigate the ultrastructure of ratite cardiac conduction fibers.
- To elucidate the relationship between conduction system geometry, cell properties, and excitation-contraction coupling mechanisms in avian hearts.
Main Methods:
- Ultrastructural analysis of ratite cardiac muscle.
- Comparative examination of conduction system and working fiber geometry.
- Analysis of gap junction size and input resistance in cardiac cells.
Main Results:
- Ratite conduction fiber geometry is adapted to varying heart sizes and contraction rates, maintaining differential conduction velocities.
- An inverse relationship exists between gap junction size and cardiac cell input resistance.
- Extended junctional sarcoplasmic reticulum (SR) in avian hearts suggests indirect calcium release for contraction.
Conclusions:
- Avian cardiac conduction systems are highly specialized for efficient electrical signal propagation.
- Gap junction characteristics influence cardiac cell electrical properties.
- The unique SR structure in avian hearts plays a critical role in excitation-contraction coupling, facilitating calcium release.