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

Abstract

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.