During muscle relaxation after a contraction, which mechanism primarily reduces cytosolic Ca²⁺ concentration to stop contraction?
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Correct answer: SERCA pumps Ca²⁺ into the sarcoplasmic reticulum
Relaxation requires removal of Ca²⁺ from the cytosol; the sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) actively pumps Ca²⁺ back into the SR, ending cross-bridge formation.
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