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Mitochondrial calcium oscillations in C2C12 myotubes.
C Challet1, P Maechler, C B Wollheim
1Pharmacology Group, School of Pharmacy, University of Lausanne, 1015 Lausanne, Switzerland.
The Journal of Biological Chemistry
|October 19, 2000
Summary
Mitochondrial calcium dynamics in skeletal muscle cells were measured. KCl depolarization induced calcium spikes and oscillations, suggesting close communication between mitochondria and the sarcoplasmic reticulum.
Area of Science:
- Cell Biology
- Mitochondrial Physiology
- Skeletal Muscle Research
Background:
- Mitochondrial calcium concentration ([Ca(2+)](m)) plays a crucial role in cellular energy production and signaling.
- Understanding [Ca(2+)](m) dynamics is vital for comprehending skeletal muscle function and dysfunction.
Purpose of the Study:
- To investigate the dynamic changes in mitochondrial calcium concentration in response to various stimuli in C2C12 skeletal muscle cells.
- To elucidate the mechanisms underlying KCl-induced mitochondrial calcium responses and oscillations.
Main Methods:
- Utilized C2C12 skeletal muscle cells expressing mitochondrially targeted aequorin for real-time [Ca(2+)](m) monitoring.
- Applied KCl-induced depolarization, extracellular Ca(2+) chelation, voltage-operated Ca(2+) channel blockade, and inhibitors like cyclopiazonic acid.
- Investigated responses to nicotinic (carbachol) and purinergic (ATP) agonists, and caffeine to probe intracellular calcium release mechanisms.
Main Results:
- KCl depolarization elicited a significant peak in [Ca(2+)](m) followed by intracellularly generated oscillations.
- Extracellular Ca(2+) influx and voltage-operated Ca(2+) channels contributed to both phases of the KCl response.
- Sarcoplasmic reticulum Ca(2+)-ATPase inhibition (cyclopiazonic acid) affected the amplitude and abolished oscillations, implicating intracellular stores.
- Caffeine induced oscillations, highlighting the role of ryanodine receptors.
- Differential desensitization and potentiation responses to repeated stimuli (KCl, carbachol) indicated distinct intracellular calcium redistribution pathways.
- Observed cross-desensitization and cross-potentiation between KCl and carbachol.
Conclusions:
- Demonstrated close proximity and functional communication between mitochondria and the sarcoplasmic reticulum in skeletal muscle cells.
- KCl-induced mitochondrial calcium dynamics, including oscillations, are mediated by both extracellular calcium influx and intracellular calcium release mechanisms.
- These findings offer insights into the physiological regulation of mitochondrial calcium and its potential implications in muscular disorders.