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Myocyte deenergization and intracellular free calcium dynamics
Q A Li1, R A Altschuld, B T Stokes
1Department of Physiological Chemistry, Ohio State University, Columbus 43210.
The American Journal of Physiology
|August 1, 1988
Summary
De-energizing adult rat heart cells increased intracellular free calcium (Ca2+) levels, primarily via Na+-Ca2+ exchange, especially when ATP was depleted. This highlights calcium regulation mechanisms in cardiac myocytes.
Area of Science:
- Cardiology
- Cell Physiology
- Biochemistry
Background:
- Intracellular free calcium (Ca2+) is critical for cardiac myocyte function.
- Understanding Ca2+ regulation is key to addressing cardiac dysfunction.
Purpose of the Study:
- To investigate the mechanisms of intracellular free Ca2+ increase in de-energized adult rat ventricular myocytes.
- To explore the role of Na+-Ca2+ exchange in calcium homeostasis during cellular stress.
Main Methods:
- Single cell fura-2 fluorescence microscopy was used to monitor intracellular free Ca2+.
- Adult rat heart ventricular myocytes were de-energized using oxidative phosphorylation inhibitors (amytal, carbonyl-cyanide m-chlorophenylhydrazone).
- Extracellular calcium dependence and verapamil effects were assessed.
Main Results:
- De-energization induced a significant increase in intracellular free Ca2+ during rigor contracture.
- The Ca2+ increase was dependent on extracellular calcium and not inhibited by verapamil, suggesting Na+-Ca2+ exchange.
- ATP depletion accelerated the rate of Ca2+ increase in sodium-loaded myocytes, indicating ATP's inhibitory role in Na+-Ca2+ exchange.
Conclusions:
- Na+-Ca2+ exchange is the primary pathway for intracellular Ca2+ influx in de-energized cardiac myocytes.
- ATP loss exacerbates calcium overload by partially inhibiting Na+-Ca2+ exchange.
- These findings provide insights into calcium handling during cardiac energy depletion.