Cytosolic Ca²⁺ Buffers

Abstract

“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 (α and β 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.