Which of the following is the 'rate-limiting step' for muscle relaxation?
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Correct answer: Active transport of Ca2+ back into the sarcoplasmic reticulum by SERCA pumps
Relaxation cannot occur as long as calcium is present in the sarcoplasm. The SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase) pumps must use ATP to move calcium against its gradient back into the SR.
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