What explains the increased concentration of Ca++ in the ER?
A-Calcium ions are actively imported from the cytoplasm into the ER.
B-Calcium concentration is kept low in the cytoplasm because of its high usage level.
C-Calcium cannot enter the plasma membrane through ion channels.
D-Calcium levels in the blood or other body fluids are extremely low.
E-The Ca ions are recycled from other molecules in the ER.
