Which event leads to muscle relaxation?
Muscle relaxation requires rapid removal of activating calcium signal and restoration of inhibitory thin filament state to prevent ATP waste. During excitation depolarization opens dihydropyridine receptors coupled to ryanodine receptors of sarcoplasmic reticulum flooding sarcoplasm with calcium that binds troponin C or calmodulin initiating cross bridge cycling. For relaxation three mechanisms lower cytosolic calcium efficiently: sarcoplasmic reticulum Ca ATPase SERCA a P type pump hydrolyzing one ATP to transport two calcium ions into lumen against concentration gradient, plasma membrane Ca
Ref: Alberts et al., Molecular Biology of the Cell 7th ed., Chapter 16: SERCA calcium reuptake leading to muscle relaxation mechanism.