What triggers calcium release from the sarcoplasmic reticulum in skeletal muscle during excitation–contraction coupling?
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Correct answer: T-tubule depolarization activating DHPR–RyR coupling
An action potential spreads along the sarcolemma and T-tubules; voltage-sensing dihydropyridine receptors (DHPR) activate ryanodine receptors (RyR) on the SR, causing Ca²⁺ release — the key step in excitation–contraction coupling.
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