Mitochondrial calcium oscillations in C2C12 myotubes.
Mitochondrial Ca(2+) concentration ([Ca(2+)](m)) was monitored in C2C12 skeletal muscle cells stably expressing the Ca(2+)-sensitive photoprotein aequorin targeted to mitochondria. In myotubes, KCl-induced depolarization caused a peak of 3.03 +/- 0.14 micrometer [Ca(2+)](m) followed by an oscillatory second phase (5.1 +/- 0.1 per min). Chelation of extracellular Ca(2+) or blockade of the voltage-operated Ca(2+) channel attenuated both phases of the KCl response. The inhibitor of the sarcoplasmic reticulum Ca(2+)-ATPase, cyclopiazonic acid, reduced the amplitude of the KCl-induced [Ca(2+)](m) peak and prevented the oscillations, suggesting that these were generated intracellularly. No such [Ca(2+)](m) oscillations occurred with the nicotinic agonist carbachol, cyclopiazonic acid alone, or the purinergic agonist ATP. In contrast, caffeine produced an oscillatory behavior, indicating a role of ryanodine receptors as mediators of the oscillations. The [Ca(2+)](m) response was desensitized when cells were exposed to two consecutive challenges with KCl separated by a 5-min wash, whereas a second pulse of carbachol potentiated [Ca(2+)](m), indicating differences in intracellular Ca(2+) redistribution. Cross-desensitization between KCl and carbachol and cross-potentiation between carbachol and KCl were observed. These results suggest that close contacts between mitochondria and sarcoplasmic reticulum exist permitting Ca(2+) exchanges during KCl depolarization. These newly demonstrated dynamic changes in [Ca(2+)](m) in stimulated skeletal muscle cells might contribute to the understanding of physiological and pathological processes in muscular disorders.
Challet
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C
Pharmacology Group, School of Pharmacy, University of Lausanne, 1015 Lausanne, Switzerland.
Maechler
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P
Wollheim
C B
CB
Ruegg
U T
UT
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology
D011189:Potassium Chloride; D002118:Calcium