In skeletal muscle, the sarcoplasmic reticulum stores a very high concentration of Ca . When Ca is released into the cytosol of muscle to facilitate contraction, it needs to be removed and pumped back into the sarcoplasmic reticulum so that skeletal muscle can return to its relaxed state. The Ca is moved from cytosol and pumped back into the sarcoplasmic reticulum where its concentration is much higher. What type of membrane transport does this represent?

Calcium ions are removed from the sarcoplasm to allow the muscles to resume their resting phase. The terminal cisternal membrane of the sarcoplasmic reticulum has calcium-ATPase pumps. These pumps actively transport the calcium ions from sarcoplasm back into the sarcoplasmic reticulum and use the energy of ATP hydrolysis for the same. As the last action potential is propagated, the calcium release channels are closed and the calcium-ATPase pumps actively move the calcium ions back into the sarcoplasmic reticulum where their concentration is higher.