Caldendrins in the inner retina.

Caldendrin is the first member of a novel family of Ca2+-binding proteins (CaBPs). Its unique two-domain structure is composed of a calmodulin-homologous teminus and an unrelated N-terminal part. The latter is thought to mediate the tight association of caldendrin with the subsynaptic cytoskeleton. Caldendrin is expressed in forebrain regions with a laminar cytoarchitecture as well as in the inner retina where it is localized to OFF cone bipolar and a subset of amacrine and ganlion cells. In addition, caldendrin is prominently present in processes and synapses of the inner plexiform layer. Thus, caldendrin-immunoreactivity is displayed by ubpopulations of most retinal cell classes, with the exception of glial cells. Caldendrin is most likely involved in dendritic Ca2+-signaling, one of the functions of its close relative, calmodulin. However, several lines of evidence suggest that due to its unique properties caldendrin might not merely substitute for calmodulin. t is speculated that either the specific enrichment in cellular micro-compartments like the postsynaptic cytomatrix, the unique two-domain structure or the altered distribution of surface charges renders caldendrin specific for distinct binding partners or certain Ca2+-triggered signaling events.