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Action potential duration determines sarcoplasmic reticulum Ca2+ reloading in mammalian ventricular myocytes
Rosana A Bassani1, Julio Altamirano, José L Puglisi
1Centro de Engenharia Biomédica, Universidade Estadual de Campinas, 13084-971 Campinas, SP, Brazil. rosana@ceb.unicamp.br
The Journal of Physiology
|July 10, 2004
Summary
Electrical activity aids sarcoplasmic reticulum (SR) calcium (Ca2+) reloading in heart cells. Ferret hearts refill SR Ca2+ faster than rabbit or rat hearts due to longer action potentials during Ca2+ reloading.
Area of Science:
- Cardiology
- Cell Physiology
- Biophysics
Background:
- Sarcoplasmic reticulum (SR) calcium (Ca2+) reloading is crucial for cardiac contractility after depletion.
- Electrical activity, specifically action potentials, influences SR Ca2+ refilling and recovery of twitch amplitude.
Purpose of the Study:
- To investigate the mechanisms underlying differential rates of SR Ca2+ reloading in ventricular myocytes from different species (ferret, rabbit, rat).
- To determine the role of action potential characteristics and ionic currents in modulating SR Ca2+ refilling efficiency.
Main Methods:
- Intact ventricular myocytes from ferret, rabbit, and rat were used.
- Sarcoplasmic reticulum (SR) Ca2+ depletion was induced.
- Action potential duration at 90% repolarization (APD90) was measured at steady state (SS) and post-depletion (PD) conditions.
- AP-clamp protocols were employed to simulate different action potential patterns during SR Ca2+ reloading.
- Ionic currents, including transient outward current (Ito), were analyzed.
- A computational model was utilized to simulate ionic mechanisms.
Main Results:
- Ferret myocytes exhibited faster SR Ca2+ reloading compared to rabbit and rat.
- In ferret, the post-depletion (PD) action potential duration at 90% repolarization (APD90) was longer than steady state (SS) APD90, promoting Ca2+ influx.
- In rabbit, PD APD90 was shorter than SS APD90, and this shortening was dependent on the preceding diastolic interval, not Ca2+.
- A larger and faster recovering transient outward current (Ito) in ferret contributed to faster SR Ca2+ refilling.
- Slowly recovering Ito in rabbit was identified as a key factor for shorter APs and slower SR Ca2+ reloading.
Conclusions:
- Faster SR Ca2+ refilling in ferret is attributed to increased Ca2+ influx during a prolonged post-depletion action potential.
- In rabbit, slowly recovering transient outward current (Ito) significantly impacts action potential duration and slows down post-depletion SR Ca2+ reloading.
- Species-specific differences in action potential characteristics and ionic currents dictate the efficiency of SR Ca2+ recovery.
Keywords:
Non-programmatic