The control of Ca2+ homeostasis: role of intracellular rapidly exchanging Ca2+ stores

The role of rapidly exchanging intracellular Ca2+ stores in the control of Ca2+ homeostasis is reviewed. The following issues are discussed: the reasons why such stores exist in eukaryotic cells; the differences between the terminal cisternae of the skeletal muscle sarcoplasmic reticulum, which have direct, physical connection with the T tubules of the plasmalemma, and the Ca2+ stores located in the depth of the cytoplasm, which are stimulated by second messengers; the cytological nature (subcompartments of the ER) of the rapidly exchanging Ca2+ stores and their functional significance. The conclusions introduce recent developments in which intracellular Ca2+ stores have been investigated also by molecular biology techniques.