Calmodulin and Ca2+-binding proteins (CaBPs): variations on a theme.

Ca2+ is a ubiquitous second messenger that frequently exerts its effects through Ca2+-binding proteins. In response to changes in the intracellular [Ca2+], Ca2+-binding proteins modulate the cellular activities of enzymes, channels and structural proteins. Multiple Ca2+-binding proteins are expressed in the retina and, in most cases, in a unique cellular and sub-cellular manner. CaBPs are retinal Ca2+-binding proteins displaying a high similarity to calmodulin (CaM). CaBPs are able to mimic some of the interactions of CaM with effector enzymes, although their physiological role has not yet been resolved. CaBPs could be cell-type specific proteins that play a key role in the Ca2+ signaling of specialized retinal neurons.