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Simultaneous Isolation and Culture of Atrial Myocytes, Ventricular Myocytes, and Non-Myocytes from an Adult Mouse Heart
Published on: June 14, 2020
High [Na+]i in cardiomyocytes from rainbow trout
Rikke Birkedal1, Holly A Shiels
1Faculty of Life Sciences, The University of Manchester, Core Technology Facility, Second Floor, 46 Grafton St., Manchester M13 9NT, United Kingdom. Rikke.Birkedal@manchester.ac.uk
Summary
Rainbow trout cardiomyocytes have a surprisingly high intracellular sodium concentration ([Na+](i)) of 13.4 mM. This high [Na+](i) significantly impacts cardiac excitation-contraction coupling via the sodium-calcium exchanger.
Area of Science:
- Cardiovascular Physiology
- Comparative Physiology
- Cellular Electrophysiology
Background:
- Intracellular sodium concentration ([Na+](i)) is a key regulator of cardiac excitation-contraction coupling, primarily through the sodium-calcium exchanger (NCX).
- Previous studies in rainbow trout (Oncorhynchus mykiss) indicated that NCX activity significantly influences contraction at [Na+](i) of 16 mM, but physiological [Na+](i) levels remained unmeasured.
Purpose of the Study:
- To measure the physiological intracellular sodium concentration ([Na+](i)) in rainbow trout cardiomyocytes.
- To investigate the effects of temperature and contraction frequency on [Na+](i) in these cells.
- To assess the implications of measured [Na+](i) for calcium influx via reverse-mode NCX during excitation-contraction coupling.
Main Methods:
- Utilized the fluorescent indicator sodium-binding benzofuran isophthalate (SBFI) to record [Na+](i) in freshly isolated atrial and ventricular myocytes.
- Measured [Na+](i) at rest and during increased contraction frequencies (0.2, 0.5, and 0.8 Hz).
- Assessed [Na+](i) across a range of physiologically relevant temperatures (7, 14, and 21°C).
Main Results:
- Reported a resting intracellular sodium concentration ([Na+](i)) of 13.4 mM in rainbow trout cardiomyocytes, with no significant difference between atrial and ventricular cells.
- Found that acute temperature changes did not affect resting [Na+](i).
- Observed a modest, frequency-dependent increase in [Na+](i) with elevated contraction rates (0.4-0.9 mM increase from 0.2-0.8 Hz), which was not significantly altered by temperature.
Conclusions:
- This study provides the first direct measurement of intracellular sodium concentration ([Na+](i)) in rainbow trout cardiomyocytes.
- The surprisingly high resting [Na+](i) suggests a significant role for calcium influx via reverse-mode NCX in cardiac excitation-contraction coupling.
- The contribution of this calcium source to contraction is predicted to decrease with increasing temperature and contraction frequency due to shortened action potential duration.