Novel compartment implicated in calcium signaling--is it an "induced coupling domain"?

Abstract

The endoplasmic reticulum (ER) is not simply a uniform continuous organelle, but is spatially and functionally heterogeneous with nonuniform distribution of endoplasmic Ca(2+)-handling proteins, such as Ca(2+)-binding proteins, Ca(2+) pumps, and Ca(2+)-release channels. Such nonuniform distribution of Ca(2+)-handling proteins is thought to create a spatially divided calcium store and to contribute to the generation of complex intracellular Ca(2+) dynamics. In addition to the particular distribution of these Ca(2+)-handling proteins within ER, extracellular stimuli may also stimulate the formation of dynamic new ER compartments containing Ca(2+)-handling proteins. These compartments containing Ca(2+)-handling proteins have potential roles in Ca(2+) signaling; specifically, they may function as "induced coupling domains" between the ER and plasma membrane, thereby allowing Ca(2+) entry into the ER.