Cytosolic Ca2+ Buffers

Ca2+ buffers, a class of cytosolic Ca2+-binding proteins, act as modulators of short-lived intracellular Ca2+ signals; they affect both the temporal and spatial aspects of these transient increases in [Ca2+](i). Examples of Ca2+ buffers include parvalbumins (alpha and beta isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Besides their proven Ca2+ buffer function, some might additionally have Ca2+ sensor functions. Ca2+ buffers have to be viewed as one of the components implicated in the precise regulation of Ca2+ signaling and Ca2+ homeostasis. Each cell is equipped with proteins, including Ca2+ channels, transporters, and pumps that, together with the Ca2+ buffers, shape the intracellular Ca2+ signals. All of these molecules are not only functionally coupled, but their expression is likely to be regulated in a Ca2+-dependent manner to maintain normal Ca2+ signaling, even in the absence or malfunctioning of one of the components.