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J Gen Physiol. 2012 Apr;139(4):261-72. doi: 10.1085/jgp.201210773.

Intracellular calcium movements during excitation-contraction coupling in mammalian slow-twitch and fast-twitch muscle fibers.

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  • 1Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104, USA.


In skeletal muscle fibers, action potentials elicit contractions by releasing calcium ions (Ca(2+)) from the sarcoplasmic reticulum. Experiments on individual mouse muscle fibers micro-injected with a rapidly responding fluorescent Ca(2+) indicator dye reveal that the amount of Ca(2+) released is three- to fourfold larger in fast-twitch fibers than in slow-twitch fibers, and the proportion of the released Ca(2+) that binds to troponin to activate contraction is substantially smaller.

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