title: Calcium regulation in photoreceptors.
abstract: In this review we describe some of the remarkable and intricate mechanisms through which the calcium ion (Ca2+) contributes to detection, transduction and synaptic transfer of light stimuli in rod and cone photoreceptors. The function of Ca2+ is highly compartmentalized. In the outer segment, Ca2+ controls photoreceptor light adaptation by independently adjusting the gain of phototransduction at several stages in the transduction chain. In the inner segment and synaptic terminal, Ca2+ regulates cells' metabolism, glutamate release, cytoskeletal dynamics, gene expression and cell death. We discuss the mechanisms of Ca2+ entry, buffering, sequestration, release from internal stores and Ca2+ extrusion from both outer and inner segments, showing that these two compartments have little in common with respect to Ca2+ homeostasis. We also investigate the various roles played by Ca2+ as an integrator of intracellular signaling pathways, and emphasize the central role played by Ca2+ as a second messenger in neuromodulation of photoreceptor signaling by extracellular ligands such as dopamine, adenosine and somatostatin. Finally, we review the intimate link between dysfunction in photoreceptor Ca2+ homeostasis and pathologies leading to retinal dysfunction and blindness.
authors.affiliation: Dept of Physiology, University of California San Francisco School of Medicine, San Francisco, CA 94143-0730, USA. krizaj@phy.ucsf.edu
authors.forename: David
authors.initials: D
authors.lastname: Krizaj
authors.forename: David R
authors.initials: DR
authors.lastname: Copenhagen
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling; D015640:Ion Channel Gating; D017136:Ion Transport; D008954:Models, Biological; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism; D012164:Retinal Diseases / Q000209:etiology / Q000473:pathology; D017948:Retinal Rod Photoreceptor Cells / Q000033:anatomy & histology / Q000378:metabolism; D014785:Vision, Ocular
chemical_list: D020746:Calcium Channels, L-Type; D002118:Calcium