<prompt> Calcium is pumped back into sarcoplasmic reticulum bySERCASodium pumpRinotidine receptorNone  <response>: Depolarization of the T tubule membrane activates the sarcoplasmic reticulum dihydropyridine receptors DHPR, named for the drug dihydropyridine, which blocks them. DHPR are voltage-gated Ca2 channels in the T tubule membrane. In cardiac muscle, influx of Ca2 these channels triggers the release of Ca2 stored in the sarcoplasmic reticulum calcium-induced calcium release by activating the ryanodine receptor RyR. The RyR is named after the plant alkaloid ryanodine that was used in its discovery. It is a ligand-gated Ca2 channel with Ca2 as its natural ligand. In skeletal muscle, Ca2 entry from the extracellular fluid ECF by this route is not required for Ca2 release. Instead, the DHPR that serves as the voltage sensor unlocks release of Ca2 from the nearby sarcoplasmic reticulum physical interaction with the RyR. The released Ca2 is quickly amplified through calcium-induced calcium release. Ca2 is reduced in the muscle cell by the sarcoplasmic or endoplasmic reticulum Ca2 ATPase SERCA pump. The SERCA pump uses energy from ATP hydrolysis to remove Ca2 from the cytosol back into the terminal cisterns, where it is stored until released by the next action potential.Ref: Ganong;s review of medical physiology, 23rd edition, page no:100 