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Optocardiography and Electrophysiology Studies of Ex Vivo Langendorff-perfused Hearts
Published on: November 7, 2019
Contraction in voltage-clamped, internally perfused single heart cells
The Journal of General Physiology
|October 1, 1986
Summary
Cardiac muscle contraction is driven by calcium influx, but prolonged depolarization also influences contraction through separate mechanisms affecting calcium stores. This study clarifies calcium
Area of Science:
- Cardiology
- Cell Physiology
- Biophysics
Background:
- Cardiac myocyte contraction is regulated by calcium ions.
- The slow inward calcium current (Isi) plays a key role in excitation-contraction coupling.
Purpose of the Study:
- To investigate the relationship between slow inward current (Isi) and cardiac myocyte shortening.
- To explore the role of depolarization and intracellular calcium handling in grading contraction.
Main Methods:
- Studied single, voltage-clamped, internally perfused guinea pig ventricular myocytes.
- Measured microscopic cell appearance and sarcomere shortening (1,000 Hz).
- Manipulated voltage steps, extracellular calcium, and holding potential to alter Isi.
Main Results:
- Isi directly correlated with the extent and velocity of myocyte shortening.
- Depolarizations exceeding the calcium reversal potential eliminated immediate shortening, associating it with tail currents.
- Prolonged depolarization increased contraction amplitude/speed over multiple beats, independent of Isi, suggesting modulation of sarcoplasmic reticulum calcium.
Conclusions:
- The slow inward current (Isi) induces and modulates calcium release from the sarcoplasmic reticulum, initiating contraction.
- A separate depolarization-dependent process, independent of Isi, regulates intracellular calcium stores and influences contraction magnitude and timing.
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