Which pumps are responsible for re-sequestering Ca2+ into the SR during skeletal muscle relaxation?

Which pumps are responsible for re-sequestering Ca2+ into the SR during skeletal muscle relaxation?

• A. Voltage-gated calcium channels
• B. Ryanodine receptors
• C. Na+/Ca2+ exchangers
• D. SERCA pumps re-sequester Ca2+ into the SR

Answer: (D)

Removing calcium from the cytosol by pumping it back into the sarcoplasmic reticulum ends contraction. This task is carried out by SERCA pumps, Ca2+-ATPases in the SR membrane that use ATP hydrolysis to move Ca2+ from the cytosol into the SR lumen. As cytosolic Ca2+ falls, troponin releases its grip on actin and cross-bridge cycling stops, allowing the muscle to relax. In skeletal muscle, the SERCA1 isoform is the main player, with regulation by small proteins like sarcolip modulating activity. Other proteins either trigger calcium release from the SR (like ryanodine receptors) or move Ca2+ across the cell membrane (like the Na+/Ca2+ exchanger); they don’t resequester Ca2+ into the SR.

Removing calcium from the cytosol by pumping it back into the sarcoplasmic reticulum ends contraction. This task is carried out by SERCA pumps, Ca2+-ATPases in the SR membrane that use ATP hydrolysis to move Ca2+ from the cytosol into the SR lumen. As cytosolic Ca2+ falls, troponin releases its grip on actin and cross-bridge cycling stops, allowing the muscle to relax. In skeletal muscle, the SERCA1 isoform is the main player, with regulation by small proteins like sarcolip modulating activity. Other proteins either trigger calcium release from the SR (like ryanodine receptors) or move Ca2+ across the cell membrane (like the Na+/Ca2+ exchanger); they don’t resequester Ca2+ into the SR.